Originally a manga by Yoshihiro Togashi, YuYu Hakusho tells the story of Yusuke Urameshi, a bitter, beleaguered, junior high punk—and legendary street fighter. One particularly bad day gets worse for Yusuke after he dies saving the life of a small boy from a car accident. He discovers that the forces of the Spirit World were expecting the boy to miraculously survive the accident but did not expect Yusuke to even be a part of it. Because of this surprising(if ultimately useless)Heroic Sacrifice, they offer Yusuke a chance to return from the dead. With the help of Botan (a perky female shinigami "Angel of Death" or essentially "Grim Reaper") and the approval of Koenma (the snarky son of King Enma, the judge of the dead in the Buddhist belief system, and the part-time stand-in for his father) Yusuke returns to the living world.But Koenma has other plans for Yusuke, as both his fighting ability and new found spirit awareness makes him a prime candidate to be a Spirit Detective, an agent of the spirit world hunting down renegade demons who threaten peace on Earth. With much reluctance, Yusuke takes on the job, and finds himself facing all manner of supernatural baddies. Lucky for him, he has the help of Botan as a liaison and tactical support. Early on in his career they send him to the Old Master Genkai, a short, crotchety old woman who nevertheless is a highly capable spiritual guru and martial artist.As his closest teammates he gathered some more-than-capable fighting partners in the form of Kazuma Kuwabara, his old school rival; Kurama, a benevolent reformed fox-spirit trapped in a human body; and Hiei, a not-so-benevolent, not-so-reformed demon who reluctantly tags along with Yusuke and his entourage as part of his sentence.During YuYu Hakusho's initial run in Japan, it was one of the few shows to compete at all with Dragon Ball Z during the early '90s. It is a classic shonen anime featuring colorful characters, lots of humor, and very clever fights. It wasn't as popular in the States as other series, but was one of the first anime to air (mostly uncut) on [adult swim], until it migrated to Toonami with an edited weekday version. However, its fans are very hardcore. It was among Funimation's earliest shows to dub alongside Dragon Ball Z, and therefore, starred some of its earliest regular cast members and kickstarted their reputation. Justin Cook, who was the Line Producer and played the lead role, is now the chief producer at the studio. In the Philippines, this animι was titled "Ghost Fighter", with the characters' names being completely different as well.
Abusive Parents: Mukuro's father is a more direct example of downright evil treatment.
Yusuke's mother Atsuko qualifies too. She beats and screams at him, no wonder he's become a punk. And for fuck's sake, she leaves the body of her dead to-be-reborn son surrounded by loads and loads of trash! It even catches fire in the end (due to an arson, though).
Adaptation Dye-Job: Color Jump pages (while admittedly a limited, sober palette) have Kurama with black hair. The anime...does not.
Togashi's own color illustrations sometimes also depict Kurama with violet hair instead of black (most notably on the second kanzenban cover), and he vacillates between having Botan as blue-haired or blonde. The anime settled on going with blue hair for Botan.
Genkai and Koenma are blond in some of the colored artwork for the manga, with Koenma's uniform being green instead of purple.
Adaptive Ability: Kuro Momotaro uses Steaming Spheres to gain an immunity to whatever attack was last used against him.
Alas, Poor Villain: The story takes a moment to focus on Byakko's shock and horror when he is betrayed and executed by Seiryuu for failing to beat his opponent. There's even a hint of a tear on his bodiless head.
Sensui's life as a Spirit Detective was not an easy one...
Even Toguro has a sad past that drove him to be the way he is.
Anti-Hero: Yusuke (Pragmatic Hero), Kurama (Loveable Rogue) and Hiei (Nominal Hero). Though Hiei could theoretically shift to Unscrupulous Hero when Yukina is involved. He also shows more heroic tendencies when dealing with Kurama and Mukuro. Kuwabara would be a normal hero in most other settings, but he's got enough hardscrabble streetfighting background to qualify here.
Arc Number: Seven for the Sensui arc. It's declared that the "seven" will dig a grave for humanity, but it's seven personalities; Itsuki remarks that Sensui saw all of his followers as expendable.
Art Evolution: The anime starts off with the somewhat 80ish type animation where characters are poorly drawn, but improves greatly by the Dark Tournament arc.
Artifact of Death: The forlorn hope can grant the user a wish, but only at the cost of their life.
The Artifact / Early-Installment Weirdness: Yusuke's Spirit Detective tools and Hiei's true demon form. In the case of the tools, they get phased out around the time of the Dark Tournament. This bit actually gets lampshaded by Botan when she laments that Yusuke never bothered to use them. In the case of Hiei's true form, he was originally supposed to be a Starter Villain, but then he got Saved by the Fans and promoted to a main character. His true form got phased out as well.
There's also the fact that putting something as vulnerable as an eye all over your body would probably work against whatever powerup a full demon form would give.
Asshole Victim: Gonzou Tarukane and Butajiri, who are both killed by Younger Toguro under Sakyo's orders. And the rest of the Black Book Club as well, for that matter. They end as victims when Sakyo (himself a member of the BBC0 has Younger Toguro kill the other remaining members when they try to stop him from completing his plan.
Assimilation Backfire: When Sensui Seven member Gourmet eats Elder Toguro to get his powers, Elder Toguro ends up taking over his body later.
Ass Kicking Equals Authority: Invoked by Yusuke and played straight by the entire demon world during the Demon World Unification Tournament arc.
Barred from the Afterlife: At the beginning, delinquent Yusuke dies saving a child from being hit by a car, which puts the Celestial Bureaucracy in a bind: He was scheduled to go to hell, but his Heroic Sacrifice partly redeemed him... but not enough to qualify for heaven. He ends up working for them fighting demons.
Bash Brothers: Yusuke and Kuwabara do this most often. Toguro and Genkai long ago might have been something between this and a Battle Couple.
Batman Gambit: Sensui kidnaps Kuwabara, supposedly so he can open the tunnel to Makai. In fact, Sensui was waiting the other heroes to rescue Kuwabara. Then he kills Yusuke to enrage his companions, crosses the barrier (it could never stop him since he has celestial energy), and then Kuwabara opens it. All this so that he could die in Makai at the hands of a powerful demon, since that would be nobler than to die of the terminal illness he already had. Said strong demon happened to be Yusuke, reborn again, possessed by the will of his dying ancestor, Raizen.
This is also Kurama's modus operandi of choice.
Sakyou pulled a pretty big one on Tarukane.
Battle Aura Seen several times in the Dark Tournament arc. Arc Villain Toguro at the higher reaches of his strength produces an aura which dissolves weaker demons. Of special note is Toguro's unwilling subordinate Bui, whose major power is literally and explicitly called Battle Aura; he uses it to fly and shoots pieces of it for attacks. The reason for Bui's insanely heavy armor is Bui's raw power is greater than his fine control, and he can't turn the aura off. The armor acts a Power Limiter to keep his aura restrained until he decides to take his armor off.
Battle of Wits: The Sensui arc focused on this for the most part, the Kaitou and Gamemaster fights being the best to define this.
The series as a whole was one of the first to exploit fighting strategically in mid battle rather than pummeling others with the superior powers.
Beam-O-War: Yusuke and Rando's Rei/Spirit Guns colliding with each other, Yusuke's Rei/Spirit Gun colliding with Chu's Suiken yoki orbs twice, Yusuke's full power Rei/Spirit Gun being canceled out by Sensui's smaller yet just as powerful Resshuu Kou Kyu Ha.
Berserk Button: Despite being a foul-mouthed delinquent who loves to fight and has trouble with authority figures, Yusuke can generally be nice to very young children (seen as early as Episode 1). Which is why he gets so royally pissed when Gouki eats a young child's soul that he'd stolen with the Orb of Baast (one of the three treasures stolen from Spirit World).
Yusuke: SPIT IT OUT! (hits Gouki in the stomach, forcing him to regurgitate the soul)
As well, Keiko serves as another Berserk Button for Yusuke.
A minor one with Mr. Takenaka with anyone trying to misrecord any correct answers for their own purpose since the reputation of Sarayashiki Junior High is in danger.
If you harm or otherwise threaten Yukina's safety, be grateful if Hiei lets you live. You better hope Kuwabara gets to you before Hiei does.
Threatening Kurama's human mother and family, or forcing him to take an innocent life will end in a very, very unpleasant fate for the perpetrator. In fact, don't threaten to harm his friends' souls and ABSOLUTELY do not defile the memory of his dead friend. And smoking a cigarette while possessing Kurama's little stepbrother is not a good idea either.
And there's Kuwabara and his whole never hit a woman thing; you try touching a woman in front of him and see the state of your face afterwards. Especially if it's Yukina. Dishonor is another button of his.
Beware the Nice Ones: It's generally not a good idea to get Kurama mad. And while Kurama acts nicest, Kuwabara is probably the friendliest in the group, and he's not to be trifled with, either, if you don't want a Jigen-tou through your chest...
The fact the merciless and brutal Blood Knight didn't want to make enemies with Kurama says a lot about him.
Sensui's main personality, Shinobu, is also fairly nice, even talking respectfully to Yusuke as if they were having tea and crumpets together. Just make sure you shake◊ his hand◊ when◊ he asks◊ you to◊.
Yukina, of all people, when she reveals she was searching for her brother to remind him he promised to exterminate all the Koorime.
Big Brother Instinct: Threatening and later possessing Kurama's little stepbrother was a very, very stupid move.
BilingualStealth Pun: The dub is littered with these for people who speak both Japanese and English. To sub fans who are monolingual in English, these lines sound like straight-up Bowdlerisation- the most infamous being "A mulberry (kuwa) is a tree, and Kuywabara's a man!"
As for the original Japanese, is it an accident that Yusuke's "Rei Gun" is, well... a ray gun?
Bigger Bad: In the manga King Enma is responsible for just about everything, in the name of keeping his public image as powerful as possible after all, Team Urameshi work for him, so if they take out a criminal, he can take credit for it.
Big Bad Wannabe: Gonzou Tarukane. While he is dangerous thanks to his wealth and his connections (being the founder of the Black Book Club, and hiring various demons and humans to do his dirty work), he overestimates his chances of winning, loses everything when Younger Toguro is defeated, and doesn't compare well to most of the antagonist's in the series. It doesn't help that The Toguro Bros were actually working for the real Big Bad, who had caused him to lose his money, and that they end up killing him after this is revealed.
Big Good: Koemna throughout the entire series. Genkai as well from Chapter Black onward.
Subverted when Hiei faces an enemy with a weapon far stronger than his sword. Blocking the thing actually cuts his sword and bracing it with his arm cuts his arm. He only gets a draw by taking a hit to make him drop his guard.
Also subverted in the final battle between Toguro and Yusuke. Yusuke sends the most powerful attack he could muster against Toguro and he blocks it and eventually stops it after an intense struggle. Toguro then dies because the strain of blocking it was equal to taking the hit.
Bloodless Carnage: A jarring moment in the Chapter Black arc. Yusuke blows a opponent's arm off with his Spirit Gun and not one drop of blood is shown. Odd because The Dark Tournament showed some fairly graphic dismemberments.
Board to Death: What happens during the Dark Tournament when Sakyo reveals his plan to open a gateway to the Spirit World to the rest of the Black Book Club, and then has Toguro kill them when they object.
Mukuro's back story went from being her father's sex slave who disfigured herself to keep herself from being molested by him in the manga to being an already cybernetic slave who couldn't remove the shackles from her arms even after she escaped and had to pay for her freedom with the flesh from half her body. Still badass either way.
Similarly, Kurama Taking The Sword in Yusuke's fight against Hiei, deliberately cutting his hand, and throwing his blood in Hiei's eye was toned down to him simply jumping in front of Hiei and backhanding him.
Bread, Eggs, Milk, Squick: At the end of the Dark Tournament Arc in the uncensored anime, right before Genkai comes back to the group, Yusuke says, "Back to skipping Detention." Kuwabara says, "Video Games." Kurama says, "My human family." And Hiei finished the series with "Various Crimes."
Cannot Spit It Out: Subverted, of all couples, by Yusuke and Keiko! According to Keiko's dad, Yusuke's favorite way to make up with Keiko after a fight is to propose marriage.
Cast Full of Pretty Boys: The True Companions' gender ratio is pretty much 50/50 somewhat skewed by Atsuko and George Saotome, though but the only girls who really get any spotlight and character development are Genkai and Mukuro. The others have their moments, but the guys are pretty much the focus of the show. There aren't many female villains, either.
Cerebus Syndrome: The manga starts out as an episodic comedy about Yusuke and Botan as ghosts trying to help the living with their problems. After a couple volumes of this, it abruptly shifts into shonen action mode. This gets far fewer complaints from fans than many Cerebus Syndrome victims, however, because most fans know the series from the anime adaption, which skips the comedic stories from the manga and rushes ahead to the action portion.
During the final arc the show suddenly becomes less action-oriented and for the first time focuses on how the events actually affect Yusuke and the gang's everyday lives, suddenly showing several episodes filled with lots character development, and quiet drama as opposed to high-speed punching and explosions.
Changed My Mind, Kid: Hiei leaves the rest of the team during the Chapter Black arc, claiming he has no loyalty to the human world. Yusuke assures everyone else that "he'll come and rescue us in the end when we need him the most". He does.
Character Magnetic Team: At the beginning, it was only Yusuke and Botan, by the Dark Tournament arc, four more members to form the Five-Man Band, six more by the end of that arc, three allies by the Sensui arc and finally over a dozen by the final arc. The majority were former enemies in some form or another.
Charles Atlas Superpower: Some of the contestants in Genkai's tournament are just normal humans, but presumably through training managed to get abilities like a Spirit Gun or bulking up his arm for a super strong strike.
The biggest one is when Koenma describes the difference between spirit and life energy to Yusuke in the fifth episode. When drained of spirit energy in the climax of the Four Saint Beasts saga, Yusuke taps into his life energy for a Heroic Sacrifice.
There was also "Goblin City" in the Chapter Black saga, a video game Yusuke plays at the arcade during the time Kuwabara is fighting Seaman. About six episodes later, guess what the team has to play against Game Master?
The Mafuukan ( Koenmna's pacifier. This also explains why he wouldn't let Ogre remove it during the Dark tournament)
The egg Yusuke throws into the fire to save Keiko early in the series is Puu!
It gets lampshaded when Koenma has to remind Yusuke about the egg during the Dark Tournament arc, as he'd completely forgotten about it after he came back to life.
Circles of Hell: Younger Toguro goes to the deepest pit of hell out of his own, complex guilt about everything.
Clark Kenting: The "mysterious" masked fighter that comes to the Dark Tournament as the gang's fifth member is obviously Genkai, even wearing the same robes as her and having her characteristically short stature. Despite this, nobody notices until unmasking time comes.
Sort of. Kuwabara flat-out asks Yusuke if Mask is Genkai, and Yusuke pretty much tells him, "That's what I thought, but s/he said no." Kuwabara is pretty firm in thinking this, until the mask gets ripped and young!Genkai is shown beneath it. Genkai's fighting style has the body's cells rejuvenated to the time they were strongest when it's used. It's... really something of a Double Subversion.
Right after Yusuke comes back from the dead he explores the town in sunglasses and messed up hair. And goes unnoticed.
In that same episode there's also a certain blue-haired fortune teller with a fake sounding accent who knows about Yusuke so you can understand why he couldn't tell it was Botan in disguise.
Clear My Name: After coming back to school, Yusuke was framed by one of the teachers in hopes getting him expelled. This was quickly cleared up after Yusuke received his first case.
Clothing Damage: Yusuke pretty much loses his upper clothing in almost all of his major fights.
Taken to its logical extreme in his fight against Yomi, where after taking a volley of energy blasts, his shirt explodes off his body. Not a fiery one, mind you, but still.
This is flat out pointed out in the actor's commentary for the episode where Justin Cook and co. discuss the characters' tendency to lose their shirts right before the aforementioned shirt explosion. They then wonder what the characters' pants are made of to prevent them from being destroyed as well.
Hiei's shirt is usually either ripped off or thrown off by the end of most of his battles.
Lampshaded by Koto: "Well, they've burned their skin, shortened their breath, and somehow lost their shirts. All in all, I'd call this a successful fight."
Cold Sniper: This role is fulfilled by the character of...Sniper. Although he's not a sniper as the idea evoke; he doesn't actually use a sniper rifle and he doesn't do alot of hiding. He can attach his spiritual energy to both his target as well as any random objects, resulting in said objects homing in on the target at incredible speeds. From dice, to rocks, to knives and forks, to even gasoline tankers. Later in the fight, however he opts for a good old fashioned pistol.
Coming of Age Story: The ending to the second-to-last episode and essentially the main point to the whole Three Kings Arc is this, as Jorge/the Narrator so explains. Supposedly, now that Yusuke is done kicking ass in Demon World, his next adventure is to allow himself to "grow up". There are also other sprinklings and hints of the "coming of age" theme throughout the series. Though mainly adhering to Yusuke, this applies to Kuwabara and Keiko as well.
Containment Field: The Kekkai barrier is used to separate the Human World from the Demon World. Unfortunately, this Containment Field only sort of acts like a net to only filter and keep out A and S Class ranked demons.
L/Ruka tries it on Hiei. She somehow manages to live through it.
Cruel Mercy: Why did Hiei spare the Ice Maidens? Because he realized they were dead inside and exterminating them would have put them out of their misery. He also does the same in the Black Tournament: when a defeated Bui asks to finish him, Hiei just tells him to kill himself and go away.
Curb-Stomp Battle: The first time Hiei fights on the good guys' side, he slashes up the guy that pissed him off before his opponent could even start to attack.
Most of Hiei battles are like that: Hiei's first battle in the Black Tournament takes a few minutes because he doesn't attack, then he incinerates his FIRE USER foe; later in the Black Tournament, Hiei faces Makintaro and cuts his arm the very moment the referee starts the match, and when Makintaro insists in fighting Hiei finishes him with a blade in the brain; against Bui, the two play a little, then, after Bui apparently wins by throwing his Death or Glory Attack back at him, Hiei unveils that such an action only powered him up and defeats Bui with a POKE and a punch; Hiei's 'battle' with Sniper consists in Hiei appearing from nowhere and piercing him with his blade; also, Hiei's battle with Sensui, only this time Hiei is on the receiving side.
Hiei isn't exactly a Fragile Speedster, but he can't take a punch as well as most of the team, and can easily attack someone's vitals, so the only question is which side of the Curb-Stomp Battle he's on.
The three members of Team Toguro apart from Younger Toguro, vs. Team Gorenja in the semifinals. Karasu blows one member to pieces before he can do much, Bui instantly dismembers his foe with his axe, and Elder Toguro, taking on the remaining three at once, defeats them all instantly, killing one and weakening the other two so that he can finish them off easily.
How about when Bakken beats the absolute shit out of an unconscious/already badly injured Kurama? Followed by Yusuke going on to curb stomp Bakken in response.
Sensui vs. Yusuke (round one, anyway), then Sensui proceeding to kick the collective asses of Youko Kurama, Hiei AND Kuwabara.
How about when Yusuke, after awakening his demon half, kicks the ever loving piss out of Sensui?
Yusuke's fight against Sniper was so very much this. In all his experience, Yusuke was always used to fighting enemies head on, but never against somebody who methodically kept his distance and chipped away at him. If it wasn't for Hiei's big damn heroic moment, Yusuke would've been dead a second time.
The battle of Shura vs his father Yomi also counts. Shura even tricks Yomi into getting in close, only to blast him point black in the face with an energy blast that resembled a nuke. Yomi didn't feel a thing. Kid never had a chance, and as Yusuke notices that he's closer to Shura's level than Yomi's, he suspects that neither does he.
Early in the series, before Yusuke died, he used to hand these out to Kuwabara every time they fought, but Kuwabara keeps coming back for more because he sees Yusuke as his rival.
Kuwabara versus Elder Toguro. Elder Toguro No Selled a few of Kuwabara's sword attacks and chipped away at him, but didn't manage to land any hits that mattered before Kuwabara literally beat him into the ground.
Darkest Hour: The Chapter Black arc is where the series takes a darker turn in general. Near the end of the arc, Sensui kills Yusuke (and Puu dies as a result). The tunnel to Demon World becomes complete. Yusuke's Heroic Sacrifice awakens greater power in his friends, who attempt to avenge his death in a three-on-one battle against Sensui, but fail nonetheless. At the end of the episode "Attempting Revenge", Kuwabara, Kurama and Hiei fall helplessly before Sensui, knowing that even after their friend's sacrifice, they still failed him.
Dark Is Not Evil: At worst, most demons play pranks on humans.) At least in the manga. For most of the series, they do seem extremely bloodthirsty. It's explained away in the manga by King Yama brainwashing demons in order to set up cases, but in the anime just has Enki "change the system" and the way demons act once he becomes King of Demon World.
Darker and Edgier: Many fans profess that the Chapter Black arc is a stark contrast with most episodes before it - and usually for the better. Included, but not limited to are some serious moral dilemmas for the characters, considerably different kinds of adversaries where simple fisticuffs won't win any fights, a deranged and disturbed villain who's not in it for the good fight, but the absolute succession of his agenda, and an overall creepier and more ominous atmosphere. Most fans would cite Chapter Black as the series at its most mature and at its peak.
Dead Sidekick: Played with during the Dark Tournament arc, where Yusuke's friends exploit the trope by faking Kuwabara's death at the hands of Toguro so that Yusuke's anger and grief will give him the power needed to defeat Toguro.
Narrator: This is our hero, Yusuke Urameshi. There's only one problem: he's dead.
Death by Irony: Gouki who eats souls for a living dies by taking a blast of spirit energy into the mouth.
Death Glare: Hiei is really good at these along with being a hostile Perpetual Frowner. However, what is truly impressive is that when really pissed off, both Yusuke and Kurama managed to pull Death Glares that make any of Hiei's look like fluff in comparison.
Demoted to Extra: After the Chapter Black Saga, Kuwabara only sits around and studies. Atsuko is another example.
Depraved Homosexual: Subverted, played around with, possibly averted and inverted with Sensui.) Played straight with Karasu.
Deus ex Machina: During Yusuke's fight with Yomi in the Demon World Tournament, Yusuke gains the upper hand when he spontaneously generates a new kind of energy. Everyone at first thinks it's sacred energy, but then Hiei exclaims that "No! It's something completely different!"
Yusuke's revival and subsequent victory over Sensui came totally out of left field when he's randomly revealed to be descended from one of the three S-class kings of the Demon World who can take control of his body at will...
Disappeared Dad: Yusuke and Kuwabara's dads, but they are both Back for the Finale. Kurama's human father is also dead, although he does later acquire a stepfather when his mother remarries.
A couple minor, "why even bother?" ones in the FUNimation dub, too.
Suzuki -> Suzuka (changed back in the remastered dub)
Shuuichi (Kurama's stepbrother) -> Kokoda
Kirishima (Kuwabara's friend with brown hair) -> Miyamoto
Sawamura (Kuwabara's friend with the buzz cut) -> Komada
Dub Text: Mostly with Itsuki. Some of his lines are completely made up. The bit about stalking Sensui(etc.) was neither in the manga nor in the Japanese version of the anime.
Also, Toguro and Genkai's relationship 50 years ago got a Relationship Upgrade from the manga and original Japanese in the dub.
Elder Toguro has a couple Foe Yay lines in the dub that weren't in the Japanese, like when he comments that Kurama's red hair isn't nearly as pretty as the silver hair he has in Youko form.
Dude Looks Like a Lady: In one of the earlier chapters, Yusuke fights a bewitching Femme Fatale who tries to use her femininity to make opponents underestimate her, trying to play on an opponent's Wouldn't Hit a Girl sense of chivalry. After a Crotch Grab Sex Check, Yusuke finds out it's just a regular guy fighter dressing like a girl to trick opponents Yusuke even berates him for not being a real transvestite, in one of the series' odder moments of open-mindedness on Yusuke's part. Miyuki accuses Yusuke of violently attacking her because of 'what she is'. He calls her out, saying if s/he hadn't been in the way of the mission, he wouldn't have attacked her at all. Starts about 6:10.
During the final chapters of the manga, the usually calm Kurama is mistaken as a girl (more exactly, everyone thinks he's Kuwabara's girlfriend), which really gets under his skin. Later, Keiko and Yusuke ask him to infiltrate a girls-only school to help them solve a case, and he nearly snaps on them.
Even Bad Men Love Their Mamas: Kurama's relationship with his human mother, Shiori, is what turned him into a decent person. He was originally planning to leave her once he regained his powers, but after she was injured protecting him, he decided to stay.
Even Evil Has Standards: Toguro refuses his elder brother's offer for assistance prior to his match with Yusuke in the Dark Tournament finals, right before smacking the crap out of him. When elder Toguro gets angry and remarks that they sold their souls together, younger Toguro responds, "That may be. But I never sold my standards.") The fact that he had basically bad-mouthed his former lover he had killed the last night and disgraced her memory didn't help at all.
Earlier, he openly condemned Botajiri's attempts to rig the match against Team Masho. He specifically wanted Yusuke to level up and give him a good challenge. He didn't care if Yusuke died before that fight, but he didn't want him out of the tournament based on a technicality.
Also, the usually amoral and even sadistic referee Koto seriously objects to two of Team Masho's member's dirty methods of fighting and Botajiri's rigging of the matches.
Yusuke's pretty much neck-deep in Foe Yay with all of his male enemies.
Everybody Was Kung-Fu Fighting: Though it starts off different, it very quickly becomes about the unusual martial arts the protagonists and antagonists use in battle, especially coming into play during the Demon Tournament arc.
Less obviously, Toguro, who is what Yusuke would become if he decided to go completely Blood Knight and forget about what he's actually fighting for.
Explaining Your Power to the Enemy: Yusuke is forced to fight someone in complete darkness. His opponent has a helmet-type device that allows him to perceive and alter the flow of energy around and inside him, a) letting him see in the dark (which Yusuke has no way of doing), and b) strengthening parts of his body temporarily. He explains all of this during the fight. The viewer is left screaming at the television for the opponent to just beat the shit out of Yusuke, which he can do with impunity thanks to the Night Vision Helmet.
For the most part, this is actually an averted trope. Explaining Your Powers To The Enemy, while it makes utterly no sense in-universe, is mainly used so the reader/viewer can understand the ability being used. In the anime, the narrator explains the abilities or items characters are using most of the time, and thus this trope stays averted for the most part.
Elder Toguro, forever bound to the branches of a tree that saps him of his Life Energy and tortured with Kurama-related hallucinations. The tree will not let go or stop until the victim's life force is drained, and as Elder Toguro has nearly unlimited regenerative powers, he will be forever bound, unable to die due to his own healing power.
Young Toguro willingly chooses one of these after his death: being sent to purgatory.
The demon who blinded Yomi spent 500 years painfully nailed to a wall of Yomi's palace.
What Hiei did to Mukuro's father in the manga. Hiei binds a special plant to him, giving a healing factor not unlike that of Elder Toguro. Hiei gives the putrid shell as a birthday gift to Mukuro to torture for all eternity. Given what the man did to Mukuro, this is a verykarmicFate Worse than Death.
Somewhat averted with Sensui. His fate: having his soul never leave his body even after death and thus being confined to eternal sleep and no afterlife, would seem like a Fate Worse than Death to most, but apparently Sensui actually finds this preferable to being judged by Spirit World in the afterlife.
Flexible Tourney Rules: Boy, are they ever and intentionally. The Dark Tournament is done as a commercial gig, so teams are allowed to negotiate their own rules and conditions for a match, which adds some variety to the proceedings and makes for a better show.
Flight: Sensui's Seikoki (Sacred Energy) allows him to fly as an angel, which is also why he's also called "Black Angel".
Earlier in the series, there's Jin, who controls and shapes wind to make whirlwinds and other various tricks. Flight is as natural to him as walking.
The Id: Toguro, who threw away his sense of right and wrong and let the Blood Knight side of his personality take over. The only reason he has anything resembling a moral code is because he hates anything that will interfere with him getting a good fight (such as Team Urameshi being disqualified on a technicality).
The Superego: Sensui, who sees the world in black and white. There is good and there is evil, with no room in between.
The Ego: Yusuke, who balances out his Blood Knight persona with a firm sense of right and wrong, and the ability to learn from experience when his personal moral viewpoint may not be correct and needs to be adjusted.
Genius Cripple: Yomi, although blind, didn't let that stop him from being the first person in the series to manipulate Kurama, who's known for being the Batman of YYH. And not only that, Yomi gets away with it.
Gentle Giant: Both Kuwabara and Kurama are the tallest members of Team Urameshi but are very compassionate.
Shinobu Sensui stands at least 6' and it would be hard to believe someone like him would ever consider destroying humanity.
Good Is Not Nice: Yusuke and Hiei can be real jerks sometimes, though they are not without their redeeming qualities. Kurama is the same way, but more outwardly pleasant and more subtle with his snarking. Kuwabara is a nice guy, though.
Good Scars, Evil Scars: Subverted. Sensui's scars are multiple, as you'd expect of a villain; however, they are entirely covered by his shirt, as you'd expect of a good guy (because he used to be one). Itsuki becomes scarred over his eye from taking Kuwabara's Rei-ken: a simple heroic scar. Mukuro's scars are also "bad guy" scars that cover half of her body; however, seeing how she got them (by pouring acid over herself to prevent her "father" from raping her as a child), as well as her usual hiding of them, makes them "good guy" markings.)
Gosh Darnit To Heck: The Viz translation is full of hilariously inoffensive language like "holy spit", "dumb cluck", and aloof badass Hiei calling people a bunch of weenies.
Groin Attack: Episode 3 had Yusuke (in his ghost state) taking control of an unconscious young teenage schoolgirl's body so that he can protect Kuwabara who was on his way to school. During his fight against the school thugs that had tried to attack Kuwabara, Yusuke (in the body of the schoolgirl) is able to battle and defeat each of them with no problem and in the end, he delievers three groin kicks to the last thug before knocking him out with a hard right punch. Afterwards, Yusuke leaves the body of the young teenage schoolgirl, who is quite shocked to see on what has transpired.
Growing Muscles Sequence: Toguro undergoes different ones, depending on the percentage of his power he unleashes. Byakko has one every time he absorbs Kuwabara's blows.
Heavy Sleeper: Yusuke early in the Dark Tournament. This is explained as Genkai's training being so strenuous, that he has to sleep a lot to recover his energies. Though it can be pretty ridiculous when he spends the entire trip to the island, all the way through the first fight in the Tournament, asleep.
Talking in Your Sleep: Despite this, Yusuke still reacts accordingly to things that happen around him. He can even fight in his sleep, having managed to knock out three opponents who wanted to take advantage of his sleeping state - and that's still on the ship.
Heel Face Return: Hiei gets caught by Yusuke for stealing from his boss, but he returns a couple arcs later as an Anti-HeroAloof Ally, and stays that way for the rest of the series.
Hell Seeker: Younger Toguro is one of these, in addition to being a Death Seeker. He chooses to be punished in the deepest level of Hell, even though he could have gotten off with a lighter sentence, because he feels that he could never be punished enough for what he let happen to his old martial-arts pupils and the aftermath of such.
Hello, Nurse!: During the Dark Tournament, a "nurse" is brought out to inspect Hiei and the Masked Fighter after the fight with the Dr. Ichigaki Team. Koenma orders Ogre to hit him on the head so that he can go see the nurse.
Heroic BSOD: During the Dark Tournament final round, where Toguro pretends to kill Kuwabara in order to bring Yusuke's Power Level to his own level, becoming a Worthy Opponent. Interesting though at this time, his Battle Aura becomes the polar opposite of Toguro's own Battle Aura, which killed well over a quarter of the stadium's spectators.
Best example played straight is Kuwabara in the Dark Tournament, where he sacrifices himself to Toguro to unlock Yusuke's full power.
—Kuwabara: Hey Koenma, you risked your life on Urameshi's fight and now I'm gonna do the same. So make a place for me, and make sure my wake is as good as his. note Of course it turned out Toguro didn't kill him (and possibly never intended to), but Kuwabara didn't know that going into it. When he realized he wasn't going to die, he played along anyway.
Yusuke attempts to invoke this during the Chapter Black arc after realizing that he's horribly outclassed by Shinobu's (Sensui) Divine Energy. His friends fail as well, though his Demonic Atavism is awakened by his second death, giving him the strength to fight with Shinobu on equal terms
Heroism Incentive: Botan bribes Urameshi with wrestling tickets to go train with Genkai, and stop a demon from learning her techniques.
Home Field Advantage: The first of the 4 Sacred Beasts, Genbu, can use his powers over earth to meld with the stone that composes the castle and move freely through it.
Homoerotic Dream: When Yuusuke is trying to come back from the dead, but needs someone to kiss him in order to transfer a spark of life energy to "jump start" him, Kuwabara gets a dream in which he does just that.
It gets better: Yusuke had to provide the dream himself (as a ghost, he could communicate through the dreams of the living, and Kuwabara is extremely susceptible. Yusuke did this to help him study for a test once). The kiss has to be from one of the three people who care about him the most who turn out to be his mother, his girlfriend Keiko, and Kuwabara, who was a big time Antagonist in Mourning. Yusuke was horrified, but he did it anyway. Kuwabara thought it was a hellish nightmare, kissing Yusuke's dead body.
Honest Advisor: Genkai to Yusuke, and Kurama to everyone, but mostly Hiei.
Yomi recruits Kurama for the purposes of his honest advice. And possibly some revenge, too, but he gives a lot of weight of to Kurama's opinions.
In a late-series one-shot, Yusuke investigates an apparent case of demonic activity at Keiko's school, but realizes that it's only two of the girls trying to force the third to leave because they don't like her performance or attitude on the team. The narrator concludes that humans are perhaps as bad as demons, and possibly worse, especially when Yusuke sells the uniform he borrowed from Keiko to someone online after she refuses to pay him because Kurama did most of the work. Which then gets subverted when Togashi's editor pointed out that Yusuke's a demon at that point.
The Hunter: The "Spirit Detective" job description.
Hyper Awareness: Yomi has six ears, and they are so sensitive that he can hear every word being spoken within the confines of his kingdom, and can even "see" facial expressions based on a person's heart rate, and can even use this ability to tell what a person is doing!
I Have Your Wife: Kurama is forced to not retaliate against Roto lest Roto order the demon stalking his mother to kill her. Kurama manages to immobilize Roto, steal the trigger to signal the demon, then kill him.
Image Song: Lots of them on the CDs. Each of the four main characters has around three or four songs by themselves, at least one song with other characters and most everyone else has at least one song by themselves.
I'm a Humanitarian: After Yusuke becomes a demon, he no longer regards the casual eating of innocent human beings as an atrocity, and casually tells his ancestor that if eating humans is what will restore his strength, he'll gladly kidnap a few innocent human beings ("really bad ones" in the English dub) and "stuff them down his throat himself" if that's what it takes to get a good fight out of him. He compares it to humans eating hamburgers, saying that a species higher on he food chain preying on one lower is just the natural order, and that humans have simply thought themselves above it.
Ironic Echo: In the Dark Tournament Arc, Kurama gets into a fight with a demonic bomber named Karasu. Early on in the fight, Karasu seems to have the upper hand and as a result mimics putting a pistol to his head and saying, "Bang", indicating to Kurama that he should just simply shoot himself rather than continue fighting Karasu. About ten seconds later, Kurama transforms into his much more powerful true form, and suddenly it's Karasu who's on the ropes. Guess what gesture Kurama decides to make this time.
It Is Pronounced Tro-PAY: Couple names in the dub: Urameshi = Yurameshi, Mitarai ('mee-tah-rye') = Mitari ('mih-tar-ee').
Laser Blade: Kuwabara's Spirit Sword. Although it is technically made out of his ki, it still greatly resembles and even sounds like a real Laser Blade.
Last Disrespects: While Kuwabara goes on a screaming fit about Yusuke dying at his funeral in the start of the manga, his outburst is a sign of genuine mourning. In contrast, their school principal calls out some teachers who are at the funeral making snide comments about both Yusuke and Kuwabara's behavior.
Level Grinding: Hiei personally slaughtered hundreds of A class demons in order to get himself to an S Class demon.
Light Is Not Good: In the manga, it turns out the reports of demon attacks were not only greatly exaggerated, they were set up and the "evil" demons were brainwashed to behave that way, THEN were captured and executed before they could talk. When Yusuke wondered how many innocent demons he may have captured, Kurama advised him to "better not think about that". This plot element was cut out in the anime.
Limited Wardrobe: Played with. Most everyone has their regular attire for the average day, but they can and do change clothes often enough depending on the situation. But their clothes usually remain assigned by color: Yusuke green, Kurama red, Kuwabara blue and Hiei black.
Literary Agent Hypothesis: The entire show is the recordings of Yusuke's career that Koenma had edited as a documentary. His right hand ogre got the job as narrator.
Load-Bearing Hero: The heroes run into a trap like this in Maze Castle, calibrated so that it takes the combined strength of all four of them to hold it up, and that anyone running out would survive at the cost of their friends' lives.
Look What I Can Do Now: Yusuke shows off his new powers after Genkai's training, and Kuwubara does the same a few episodes later.
Made of Iron: This being a shounen series of course, practically every single character absorbs insane amounts of punishment, though usually offenses that produce cutting force seem much more effective at putting people down. Kuwabara however really takes the cake out of the main cast: being not as agile or as quick as Yusuke, Kurama and Hiei are, he tends to get hit a lot in his fights, which does little if anything to shorten them; no matter how many of his bones you break he just takes it and gets back up for more. He frequently deals out such nasty hits that one foe literally ran away from him as the prospect of pummeling him over and over again to no effect while attempting to dodge his Reiken for another thirty minutes.
A more literal example, Gouki almost literally claiming his skin is as hard as steel.
Magnificent Seven: Subverted and inverted with Sensui's group and Sensui's own personalities
Maybe Ever After: Hiei and Mukuro. It was originally intended to be less vague, but shipper backlash caused it to end the way it did.
Meaningful Funeral: Yusuke's in the first episode. Seeing how much he truly meant to everybody convinced him to undergo the trials to regain his life.
Meaningful Name: "Urameshi" is what Japanese ghosts who are haunting a house wail; "Kuwabara kuwabara" is a charm against ghosts; "Kurama" and "Hiei" are Japanese mountains said to be sites of demon activity; all of the ferry girls have names associated with flowers and plants ("Botan" peony, "Ayame" iris, "Hinageshi" poppy). This plant naming even goes for Sensui, whose name is a kanji anagram of "suisen", "daffodil") and Itsuki ("flowering tree"), perhaps to note the severity of their Face-Heel Turn.
Mt. Hiei was forbidden to women until recent history; Hiei turned this on its head by being born on a floating mountain where men are the ones who are forbidden.
Meddling Parents: Raizen when he possesses Yusuke during his final fight with Sensui.
Mind Rape: Chapter Black is supposed to be watched along with Chapter White to get a balanced look on humanity's potential for great good and great evil. Watching just Chapter Black by itself will drive you nigh insane.
Monstrosity Equals Weakness: All over the place. Generally, humanoid enemies are real threats, while more monstrous ones are just cannon fodder.
Inverted by Younger Toguro, who is at his ''weakest' when he looks completely human.
Mook Chivalry: the big groups of monsters don't just all attack at the same time, but for drama's sake they always fight one on one.
The Movie: There's two - A half-hour one and a feature length one.
Also the quiz game between Kaito and Game Master. Sure it's a multiple choice test of general knowledge. But then they go to memorizing the whole question database to recognize a certain question with just the first word and press the buzzer or even memorizing the complex formulaic pattern the questions follow to hit the buzzer before even the first word to answer... correctly every time.
Muscles Are Meaningless: Played straight and subverted: Kurama and Genkai possess enormous strength but both are fairly thin, while each time Toguro powers up, his musculature increases, and each of his common levels 20%, 30%, 45%, 60%, 80% give him a relatively identifiable build.
Unlike a lot of shonen, the general build of each character does not change as they become stronger. In fact, with the exception of Toguro the size of your muscles have no bearing on actual strength. Explained by Genkai that the physical body has its limitations, but the augmentation of spirit power to their body is crucial.
What's odd is that when Toguro powers up completely, Kurama even says, "The structure of those muscles...ingenious." And then absolutely no character around or above Toguro's level follows suit.
Nice Job Fixing It, Villain: Of course, Yusuke's second death led to him being revived as an insanely-powerful demon hybrid that later defeated Sensui.
During the Dark Tournament, Elder Toguro could have easily killed Kuwabara in a single attack, and he wouldn't have even seen it coming. However, he instead chooses to Mind Rape him by telling him that Genkai has been dead for two days and his friends hadn't told him, and that allows him to find the strength to defeat Elder Toguro for Genkai's honor.
Not Just A Tournament: The Dark Tournament ark is already pretty, well, Dark, but then it is revealed that the true purpose is for betting and power brokering behind the scenes. The later Demon World Tournament is a complete aversion of this trope, especially considering where it takes place.
Not So Different: A major underlying theme of the series is that humans and demons and really Not So Different. At first it seems that demons are made out to be Always Chaotic Evil. But later we find many humans in the series who are actually worse and many demons who truly have a good heart at least deep down. The case is brought even further in Chapter Black. Then at end of the manga, it is revealed that in the past, spirit world residents actually made demons look evil so they can rule, not to mention, King Yama brainwashing them. This later became a norm so demons have no obligations of being good and usually turn out evil. But whether you are human or demon, you would have just as much potential in good or evil. Well at least in this show.
Oblivious Younger Sibling: Shuuichi, Kurama's little stepbrother, is completely oblivious to his brother's demonic heritage and supernatural activities.
Odd Friendship: Kuwabara and Hiei. Hiei constantly belittles how much of a dumbass Kuwabara is while Kuwabara keeps up with the short jokes. Kurama even jokes about how one day they might even become in-laws.
Oddly Small Organization: The underworld's cleanup squad for when things go wrong consists of one detective and any friends he might make along the way. Though this is rendered a bit moot by the manga's ending, where it was revealed that Yusuke might not have been needed as badly as we originally thought.
Off Model - some scenes in the anime has this. For instance, there's a tendency for Sensui to have a really weird, long neck.
In the final volume, Togashi pretty much pairs off EVERYBODY. A rundown:
Hiei and Mukuro is implied but still leaves room for speculation. Kuwabara and Yukina is made much more likely. Yusuke's dad comes back into the picture and gets back with his mom. Chu falls for a new character named Natsume, who eventually returns the sentiment. The trio of Juri, Koto and Ruka admit to loving the trio of Jin, Suzuki and Touya. Koenma and a female reaper also are implied to get together.
Oh Crap: Pretty much any time Toguro shows up is an "Oh crap!" for someone.
Bui gets a literal Oh Crap moment during his fight against Hiei.
Opt Out: Kuwabara didn't participate in the final arc, instead deciding to focus on his academics.
Oral Fixation: Koenma's pacifier, not so out of place in his infant form but much more noticeable in his older and more Bishōnen guise. Apparently, several centuries of soaking in a junior god's essence also makes it a potent magical object.
Passive-Aggressive Kombat: Kurama, at least twice; at the end of the Four Saint Beasts arc, Hiei mentions how he always has to have the last word; and more literally at the beginning of the Sensui Arc.
Physical God: Any S Class fighter. Sensui himself stated that he can't even use 1/5 of his full power because to would put too much stress on the planet. Thankfully the Demon World is much more bigger and durable.
According to Sensui, A Class demons have power roughly equivalent to the gods of various religions and myths (in the dub, he states that they are on par with the Titans of Greek mythology).
Psychic Static: Yusuke does this to Murota. It might be considered a slight subversion; he concentrates simply on exactly what he intends to do. Unfortunately for poor Murota, a straight jab from Yusuke is enough to put him through the wall even if he sees it coming.
Random Power Ranking: The classifications for power are (increasing order) D, C, B, A, S. note The classification is set up by the Spirit World, so S-class means "anything the Spirit World fighters can't handle", which goes from those just above A-class to true warrior gods whose powers make weak S-class demons look like nothing.
Rock-Paper-Scissors: First appears as one of Genkai's tests and after that happens with Kuwabara throughout the series.
Running Gag: Several times Koenma has appeared right behind Yusuke, speaking to and startling him in the process. Botan does this to Yusuke once as well. The entire gag got subverted toward the final matches of the Dark Tournament arc, where Yusuke's spirit/reiki level became powerful enough to enable him to detect Koenma's presence as soon as he turns up.
Also Yukina being Hiei's sister. But Kuwabara doesn't know. The other characters like to poke fun at this.
Sacrificial Revival Spell: This was Kurama's reason for stealing the Forlorn Hope, a magic mirror that grants any wish, but kills the user to do so. He was going to use it to save his terminally ill mother. Subverted in that Yusuke prevents this by joining him in the wish, so the Forlorn Hope takes half of their lives to save her.
School Uniforms are the New Black: Before the The Dark Tournament, Yusuke, Kuwabara, and Kurama would go everywhere in their school uniform. This includes joining a contest to become the pupil of an Genkai in the mountains, attacking the castle of demons intending to take over the human world, and raiding the mansion of a evil rich guy to rescue a Mysterious Waif.
Yusuke is an interesting example in that his 'uniform' is not in fact the school uniform since he specifically wears the wrong color as a form of rebellion.
Secret Test of Character: Played perfectly straight when Yusuke is faced with the dilemma of killing his mentor to learn her ultimate technique, he refuses, but not immediately. Good thing, too, because if he had refused without hesitating, he would have failed the test as it would have indicated a lack of desire to get stronger.
Genkai loves these: the screening process for the role of her apprentice is full of them, though geared towards strength and ability rather than morality. An ordinary lottery that actually gauges power, seemingly normal arcade games that are altered to gauge spiritual attributes, a booby trapped forest that only seems like a labyrinth to those who don't have the awareness to travel through it, etc.
And early in the series when Keiko is caught in a fire, he was told that he could sacrifice the energy he was collecting in his spirit egg (the means by which he could return to life) in order to lead her to safety. He did so without hesitation, which impressed Koenma so much that he offered Yusuke another chance to return to life. Of course, he also had plans to make Yusuke the next Spirit Detective.
Sempai Kohai: Yusuke was being sarcastic when he called post-Face-Heel Turn Sensui 'sempai', but he's notably more respectful to happily retired Kuroko Sanada than he is to anyone, ever.
Senseless Sacrifice: The absolute worst part of Yusuke's (first) death is that the child he saved was supposed to miraculously survive anyway. Yusuke literally died for nothing.
Botan tells him that if Yusuke hadn't shoved the kid out of the way, the little boy would have gotten one less scrape. So Yusuke's sacrifice actually made things worse. Luckily for him, it's the thought that counts.
Serial Escalation: Many, MANY times. The younger Toguro maxing his power to 120% is a good one to cite.
Shoot the Shaggy Dog: The entire Chapter Black saga is an example of this, partially due to Sensui's Batman Gambit above, and partially because Team Urameshi put so much effort into stopping something that the SDF could have done on their own. And Yusuke died, but got better.
Shout-Out: During the Dark Tournament, there was a shout out to Super Sentai of all things (it's one of the teams ruthlessly offed by the Toguro team; they even use the Himitsu Sentai Goranger codenames). Also in a manga-exclusive story, Kurama throws a rose in front of two rival gangs a la Tuxedo Mask.
There are actually quite a few Shout Outs, one of the biggest being how Yusuke dies in the beginning. He saves a child who ran out into the street with a soccer ball, only to later be told that the soccer ball would have cushioned the child, saving the boys life without leaving a scratch on him. This is a situation that would have, without Yusuke's unfortunate intervention, been exactly the same as what happened to Tsubasa in Captain Tsubasa.
Not to mention when Kuwabara goes to the 'Megallica' concert in episode 75.
When Yusuke and Kuwabara are arguing after their first arrival at Genki's house, several Street Fighter characters can be seen, including Dhalsim, E. Honda, Zangief (with a scar on his chest instead of all the hair), and middle aged Ryu.
Sorting Algorithm of Evil: Every new bad guy the heroes go up against is billed as really strong and evil, but after a while, the show makes you ask why Spirit World placed such top priority against nobodies like Kurama and Hiei in the first season.
The first case is actually excused, as these "nobodies" stole valued objects from King Enma's collection. Koenma states that, should his father find out, the consequences of his rage would be such that even the Human World would feel them.
It actually works with a bit of Fridge Logic. Because of the barrier, S class and A class demons can't cross over. So a high B (Toguro) IS the strongest force imaginable, but not someone you would send the new guy after (why Yusuke never heard of him). Sensui was an unknown threat (at least in the dub, Koenma thought he was just some crazy guy who disappeared) and all his forces were strong in different ways (the introduction of territories) and had only activated a few months prior. As for anything beyond Sensui: Those were A and S class demons who would never have been a problem because of the barrier. It is sort of like how a cop doesn't have to worry about someone with a nuke (for the most part).
The show is considered to have one of the most broken algorithms in anime because it started to follow the Dragon Ball Z pattern of being completely outclassed by the next Big Bad. The first few major fights Yusuke won by luck (i.e. having moss in his ears and making Rando Hoist by His Own Petard), but once he Took a Level in Badass there was no reason why each set of villains was more powerful than the last.
Lest we forgot, final season revealed that Toguro, the biggest Dragon the series had up to that point, was only a B-rank demon.
It's probably Toguro who really kills it. Up until that point, all of the antagonists were relatively equal, to the point that Hiei completely destroyed the penultimate Saint Beast. Then Toguro shows up and he's completely above and beyond anything they've faced, actually pretending to lose. Then he comes BACK and reveals that he was only at 20%. While the Dark Tournament competitors were probably on a steep power slope, there's no real indication. Yusuke goes through not one but two sudden power-ups to defeat Toguro, & he keeps those power-ups, so the other bad guys need to get stronger. Oddly enough, Sensui admits to being weaker, just more experienced until his seventh personality breaks out the sacred energy. Even Toguro only being a B demon isn't so bad, until they actually GO to Makai and A classes suddenly become red shirt armies while low-to-mid S-classes can take on hundreds at once & supposedly have planet-exploding power. It gets so bad that new characters have to come out of nowhere to claim the title of strongest.
Spontaneous Weapon Creation: At one point, Hiei uses his ability to create a sword made out of Dark Fire. He's reluctant to use this more than he can help though, since it reminds him too much of Kuwabara's Spirit Sword.
Story Breaker Power: Raizen is stated to have once been the most powerful demon in the entire series. His power was so great that the other Two Kings of Demon World could be easily defeated if he was currently in his prime. What is preventing Raizen from using this power? He's starving. Raizen's power comes from eating human flesh and he gave up the practice hundreds of years ago. Notably on his death bed Raizen still has S class demon power on par with Yusuke's current powers who as far as S class demons are concerned is a runt in the litter.
For perspective Kurama talks about how there are some demons that are so powerful that even the S Class ranking (the highest level of demon) doesn't properly describe their power level, these kind of demons are more accurately described as gods rather than demons. Raizen is said by everyone who knew him in his prime as the most powerful demon that had ever lived and that his power was so great that his enemies would "piss their pants" if they saw him in action. Definitely counts as story breaking power.
Supernatural Gold Eyes: Kurama may look like a red-haired, green-eyed young man in his human form, but as soon as he drops the human disguise and turns into his real demonic form, his eyes change to this color. Itsuki also has this type of eyes, and they are a hint that he isn't exactly a human psychic. Elder Toguro has them too.
Superpowered Evil Side: Subverted with Sensui's Kazuya personality which is still technically weaker than his main personality. Possessed Mazoku Yusuke.
Teen Pregnancy: Atsuko is 28 when Yusuke dies, meaning she was only 14 when he was born.
Teeth Flying: Happens off-screen in an early episode of the dub. Kuwabara is set upon by a group of thugs while he's taken a vow not to fight at all, even in his own defense. As Yusuke and Botan watch helplessly from the sidelines, Botan makes the horrified observation, "Is that a tooth?".
Slightly subverted in that, while it wasn't shown in actual combat, Kuwabara could have surpassed everyone's intelligence in the end and he happened to have the one super weapon that could slice through a class S armor that also didn't weaken as he stopped fighting since it's the in-universe equivalent of Muramasa.
It's implied that Mr. Akashi was hoping Kuwabara would hit him for changing his test to give him a failing grade, so that even if his deception came to light, Kuwabara would still have violated his end of the bargain.
Xanatos Speed Chess: Just about all of Kurama's fights. While he usually has a vague plan going in, he almost always has to rely on a stroke of genius to save the day.
Yaoi Guys: Karasu, Itsuki. Sensui is debatable, since he's not very preoccupied with relationships beyond using people while trying to destroy humankind... but there are very subtle cues in his backstory and in the way he acts.
Yin-Yang Bomb: Toward the end of the series, one of the characters mixes human energy and demon energy. The resulting combination is far more powerful than the two were separately.