Genius Bruiser: In school, his best subjects were Physics and Music. He's also knowledgeable in anatomy and first-aid, which allows him to treat his own wounds or and target vital spots while fighting.
Invincible Hero: Subverted. While Riki is inhumanly strong and wins against most of the enemies he faces, there are multiple moment where he struggles and nearly dies even.
Aneyama shoots him with a special bullet which weakens Riki-Oh's strength to less than a boy's. After a chapter-long Humiliation Conga, he gets Akuta to help him remove the bullet to restore his strength.
His first fight against Mukai goes poorly because in his heart, he's built up Mukai as the ultimate Invincible Villain. After meditating for several days, he properly disciplines himself to face Mukai once again for a proper Final Battle.
Nachi
Big Brother Instinct: Technically, he's the younger brother, but after his death, his spirit does not take kindly to Baron Corpse attacking Riki.
Brainwashed and Crazy: It's implied that the man at the head of the story's over-arching conspiracy had a hand in shaping him into what he later becomes.
Dark Messiah: The denizens of the Cape see him as a saintlike healer; however, it's implied that there's something unbalanced behind the saintly visage. There is. Big-time.
The Mentor: After his death, his spirit becomes this to Riki-Oh during the "Palace of Eternal Youth" arc's climax.
Physical God: The people of the Cape referred to him as the "Living God".
Red Right Hand: His left hand has a swastika embedded onto it and is the source of his psychic powers.
Woobie, Destroyer of Worlds: He was abandoned by Riki-Oh while playing Hide and Seek, and now he's practically trying to wipe out the human race.
Cho Zenki
Old Master: He was a bodyguard of Chiang Kai-shek when he was younger and he's imparted his skills to at least two disciples. This man taught Riki-Oh everything he knows about martial arts and age hasn't slowed him down much.
Big Bad Wannabe: Anime-only, due to being a a lot physically weaker and not skilled in martial arts.
Cruel and Unusual Death: Like the film, his fight with Riki-Oh ends with him running afoul of a meat grinder.Unlike the film, though, Riki pulls the Warden out before he can lose more than his legs, but he still bleeds out from these grievous wounds.
Even Evil Has Loved Ones: Despite being a very evil man, he has a son that he genuinely loves and cherishes.
Four Eyes, Zero Soul: His dark glasses and lack of humanity towards the prison's inmates combine to give him this trope.
Hate Sink: A cold hearted and sadistic scumbag who sees other people as nothing more than things to be ruled over.
No Name Given: He’s only known as The Warden in the story, his true name was never revealed.
One-Winged Angel: He becomes a Hulk-like giant whilst fighting Riki-Oh. He says he was able to do so by training his muscles with Kokiko (essentially Qigong).
You Have Outlived Your Usefulness: Invokes this on one of the prison's enforcers after the latter fails to kill Riki. Later, he does the same to Sugiyama.
Used to Be a Sweet Kid: He used to be a compassionate and well-meaning child who's response to finding out that he couldn't be a doctor because of his sickly body making it so that wouldn't be able to live past 20 was to instead aim for becoming a lawyer so that he could protect the week, but when Zenki praised his good intentions and took him in as a pupil, he wound up becoming corrupted by the power he gained from the training he underwent, leading him to become the cruel tyrant he is today.
Sugiyama Tokuzo
0% Approval Rating: He is loathed by all the prisoners, including The Warden, who kills Sugiyama for getting in his way when he is about to shoot Riki-Oh.
Big Bad Wannabe: He is rather incompetent and cowardly despite his sadistic and ruthless persona.
Dirty Old Man: He has a collection of porn in his office.
The Dragon: To the Warden. However, it becomes clear by the end that he's nowhere near as dangerous as his boss.
Laughably Evil: He can be rather buffonish and cowardly at times, which makes him quite clownish.
"Pop!" Goes the Human: His death, courtesy of being shot by the Warden's customized pistol and its compressed-gas rounds.
Red Right Hand: One of his hands is missing, replaced with a prosthetic hook.
Iwata
Asshole Victim: He is such a nasty piece of garbage, that when Riki kills him, it is satisfying and cathartic.
Hate Sink: He is despicable, vile and nasty in every way possible.
Jerkass: A loathsome piece of shit who bullies weaker prisoners.
Kick the Dog: He deliberately destroyed a toy made by Wakamatsu who was going to send it to his son.
Starter Villain: He and Bandoh are the first opposing force that Riki-Oh faces in the manga. Neither lasts very long.
Too Dumb to Live: Given that Riki-Oh took out his hired muscle with ease, trying to stab him from behind with a nail probably wasn't the best thing that Iwata could have done.
Wakamatsu
Bully Magnet: He frequently gets bullied by other prioners for being so nice.
Driven to Suicide: Eventually, he can't take any more of the abuse and hangs himself.
Mercy Kill: He shot 119 of his own men that were slowly dying from a gas attack, claiming that death was the only mercy he could give them. He keeps a rose garden containing a flower for each of his fallen men.
Rasputin Death: He has his arm chopped off by Riki-Oh, then gets punched through the stomach by Riki-Oh, causing his insides to come out. Washizaki is still alive in spite of all that, until Nachi vaporizes him.
Villain Decay: Built up as the big bad of the Cape Arc by being the leader of the cape and easily defeating Riki-Oh in a fight yet his later insanity leads him to become a much easier opponent for Riki to take down.
Hate Sink: A fat, repulsive and sadistic maniac with a complete lack of emapthy.
Kevlard: His body fat can not only absorb the force from Riki-Oh's punches, but suck in the arm used to throw said punch. He claims he can break people's bones this way, too.
Verbal Tic: He says "Zura" at the end of his sentences.
Mizuguchi
An Arm and a Leg: A somewhat mild example—when Aneyama punishes him for failing to kill Riki-Oh in the past, Mizuguchi ends up losing his nose during the ensuing torture.
Asshole Victim: He gets tortured by Aneyama for failing to kill Riki-Oh. Considering that this happens after we learn about his more unsavory aspects, it's hard to feel sorry for him.
Cold-Blooded Torture: He's implied to indulge in this, as he threatens Riki-Oh with brutal dismemberment before death, and delights in the idea of Riki-Oh being force-fed sulfuric acid.
Faux Affably Evil: He's introduced as a rather pragmatic, laid-back gangster who took the daughter of one of his underlings under his wing after Riki-Oh killed said underling in a duel. Before the arc is finished, however, this relatively nonchalant facade is revealed to be masking some ratherunpleasant habits...
Hate Sink: There's not a single shred of humanity or sympathetic qualities in Mizuguchi.
I Am a Humanitarian: It's implied that his chef includes human sashimi as part of his diet.
Killed Mid-Sentence: He's slain by one of his own lieutenants just as he's about to give up the same of Riki-Oh's true father.
Non-Action Big Bad: Despite trying to blow Riki-Oh up with a rocket launcher in his introduction, he's ultimately helpless when Riki-Oh confronts him after killing off his lieutenants.
No Kill like Overkill: When he first shows up to kill Riki-Oh, he brings a damn rocket launcher to do the job. Of course, considering that Riki-Oh survived being shot five times when he tried killing him in the backstory, this might count as just being prepared.
Dumb Muscle: Subverted—while he's hardly a smart man, he's insightful enough to recognize that Riki-Oh's carrying a lot of grief beneath his grim demeanor, and pities him for it.
Even Evil Has Standards: Even when he was a full-on bad guy, he couldn't work directly under Mizuguchi after the crime lord orchestrated the mass murder of orphans and the homeless with poisoned food.
Heel–Face Turn: Introduced as an Elite Mook for a low-level gangster, but chooses to follow Riki-Oh for the Mizuguchi arc.
Heroic Sacrifice: When both he and Riki-Oh are mortally wounded by one of Mizuguchi's lieutenants, he chooses to give Riki-Oh a crude form of blood transfusion so that he might live...at the cost of his own life.
Asshole Victim: After he commits suicide, absolutely no one sheds a tear for him.
Cold-Blooded Torture: He takes sadistic delight in tormenting his victims—in the backstory, he tortured Riki-Oh's adoptive father and grandfather; in the story proper, he punishes Mizuguchi rather savagely for failing to kill Riki-Oh in the backstory. Long story short, it involves a power drill, a hollow tube of bamboo, and boiling soy sauce.
Creepy Crossdresser: Downplayed at first, with his penchant for nail polish and lip gloss. However, in the climax of his arc, he goes to wearing a full-out bridal kimono in honor of his deceased sister.
Berserk Button: Don't do anything uncouth in his presence, like leave a hair in his tea. Or mention his true age.
Depraved Homosexual: He has a creepy fascination with Riki-Oh at first. Later, this is lost beneath a hateful desire to see Riki-Oh dead.
Disproportionate Retribution: His butler leaves a hair in his tea. Aneyama's response is to butcher him with a razor-edged ceiling fan. Later, when another of his servants accidentally makes a remark about Aneyama's true age, the enraged villain kills him with another remote-controlled death trap.
Even Evil Has Loved Ones: There is ONE human on the planet he cares about. His long-dead sister.
Expy: His sadistic, psychopathic personality, effeminate behavior and the design of his eyes all make him quite reminiscent to Freeza.
Hate Sink: Like the other villains, Aneyama is designed to be a truly loathsome and despicable character. Even his love for his deceased sister does absolutely nothing to make him come off as sympathetic.
Villainous Breakdown: He begins to steadily lose it when Riki-Oh begins tearing apart his operation. At the very end, he completely loses his head when his cosmetic surgery is destroyed, leaving him as an ugly old man, and throws himself off a cliff to his death.
Akuta
Disney Death: He's on death's door when Aneyama's "Crystal Night" plan goes into effect. Riki-Oh is guided by Nachi's spirit to use the power of his six-point-star hand to save the kid's life.
Tag Along Kid: Notable, because he's the last of Riki-Oh's companions who follows him for the remainder of the story.
Bill Hickok
Ace Pilot: He's able to fly his plane through regions that would cause lesser pilots to crash. This makes him a key ally to Riki-Oh, as Mukai's domain is in a part of the Arctic Circle that screws up the instruments of most planes.
Crouching Moron, Hidden Badass: He comes off as a laid-back drunkard, but he's one of the best pilots in the sky, and a pretty good fighter too.
Jerk with a Heart of Gold: Abrasive and rough around the edges, but he's a nice guy once you get past that.
A God Am I: He seriously believes himself to be God.
Dark Messiah: His most direct servants view him as a living god, and worship him devoutly. He was literally created to be this by the people of the future.
Death Seeker: After Riki-Oh forgives him, Mukai is overcome with remorse. Unable to bring himself to kill his own son any longer, Mukai begs Riki-Oh to strike him down.
Full-Frontal Assault: He confronts Riki-Oh in the nude in their first duel. Partly because he just finished bathing, and partly out of the "unconcerned with human expectations" variety.
Luke, I Am Your Father: He is Riki-Oh's biological father...as well as his descendant from the future.
Nigh-Invulnerable: Riki-Oh (almost) couldn't make a scratch on him, probably helps that he's immortal.
Not So Invincible After All: Despite losing badly, Riki-Oh manages to land a small cut on his cheek. This shakes him badly enough that he gets nightmares from it.
in his anus to try and stab Riki-Oh with.