Osiris Red. The top student at Duel Academia and the series protagonist, whose character in Season 4 is practically unrecognizable from his character in Season 1, due to a brutal Break the Cutie arc in Season 3 and being used to demonstrate the realistic psychological trauma of many tropes from the original series and shonen anime heroes in general on a kid.
Voiced by: KENN (Japanese) and Matthew Charles (English)
Almighty Janitor: Is Osiris Red, the lowest tier that is mocked for being full of stereotypical losers, but is the best duelist in the academy.
He can top deck the exact card he needs several times per duel. If he has no hand, he'll probably draw Bubbleman, Fifth Hope, Pot of Greed, or something that lets him draw more cards — and it's not uncomming to draw something that lets him draw even more. Any time he ever plays A Hero Emerges his opponent will always pick the one card in his hand that would save him. And if he uses a card like Card Trooper to mill cards from his deck, every single time he does one of the milled cards is Necroshade or Necro Gardna, and you can bet he has a card ready like Miracle Fusion or Miracle Contact to use the other cards sent to the Graveyard for a Fusion Summon.
For a perfect example of his impossible luck, there's his duel with Saiou at the end of Season 2. He uses Fifth Hope to draw 3 cards with no other cards in his hand or on the field. He draws Neo Space, Silent Doom (which he uses to revive Elemental Hero Neos), and Neo Spacian Gran Mole, thus pulling Elemental Hero Grand Neos from nothing. When he attacks and when Saiou destroys Grand Neos using a card effect that allows Jaden to draw a card, what does he draw? Reverse of Neos, a Quickplay Spell so he can activate it during the Battle Phase, and it summons Neos back from the deck with a power boost, just enough to destroy Saiou's monster and win the duel. And if you're wondering, yes, this was the first time Reverse of Neos and Fifth Hope were ever shown.
His ridiculous luck also applies out of the duel. In Episode 4, he helps the owner of the campus card shop with her packages and for his good deed gets a few free cards. It just so happens that one of those cards is Transcendent Wings, which he just happens to draw in his duel with Manjoume and use it along with Winged Kuriboh LV10 to win.
His opponents also have a nasty habit of running into the Idiot Ball/Villain Ball. In the above example Manjoume could have used the ability of his VWXYZ-Dragon Catapult Cannon to banish either Winged Kuriboh or Transcendent Wings, but he instead just attacked.
Plot Armor: Thanks to the Magic Poker Equation you could make a drinking game out of how many times Judai goes against an opponent with a better deck and wins through sheer luck, but after Season 1 you'd need a liver transplant.
Introduced in Season 3; the top student of North Academia and owner of the only set of Gem Beast cards. He quickly becomes Judai's best friend and closest partner in the struggle to save reality in Season 4.
Voiced by: Kanako Irie (Japanese) and Christopher C. Adams (English)
Judai's original best friend and Sidekick, a role he fights to keep in Season 2 but gradually leaves behind to pursue his own Character Development in Seasons 3 and 4.
Voiced by: Masami Suzuki (Japanese) and Wayne Grayson (English)Juudai's best friend and sidekick, Sho Marufuji (U.S. name: Syrus Truesdale), whose feelings for his friend toe the line between brotherly and Ho Yay (if anything, this is exaggerated by several lines of dialogue in the dub, and has netted him rivals for Juudai's attention/affection in the form of Tyranno Kenzan and Overseas Champion Johan Andersen); he has unquestionably had the most Character Development of all the characters, symbolized by his promotion to a higher dorm every season.
Ra Yellow. Enters Duel Academia in Season 2 and decides to become Sho's rival for the role of Judai's "little brother."
Voiced by: Hiroshi Shimozaki (Japanese) and David Wills (English)Tyranno Kenzan (U.S. name: Tyranno Hassleberry), introduced in Season 2, a dinosaur-obsessed student with actual "dino DNA" flowing through his veins from an accident (and for some reason fancies himself a wannabe Army drill instructor in the dub). Originally fought with Sho over Juudai's attention (and affection), but quickly found a new rivalry with fellow fossil enthusiast Jim "Crocodile" Cook in Season 3.
Verbal Tic: Ends sentences with "-saurus!" and "-don!" in the original.
Jun Manjoume (Chazz Princeton)
Obelisk Blue/Slifer Red. Judai's first rival. Originally a rich snob who looked down on everyone else, he went on a short journey to find himself in Season 1 and came back much more honorable, despite his attempts to hide it, and determined to succeed because of his merits and skill rather than his money.
Voiced by: Taiki Matsuno (Japanese), Tony Solerno (English, Episode 1-89) and Marc Thompson (English, Episode 90 onwards)The Rival and Worthy Opponent to Judai. Though initially a high-ranking member of Obelisk Blue, he experiences a losing streak and drops out, going on a journey to find himself and ending up at the North Academy duelling school. Though he rejoins Duel Academy, he is forced to start over at Slifer Red and decides to keep wearing his black North Academy uniform. He eventually makes it back up to Obelisk Blue.He also has the power to see and hear monster spirits. Unfortunately, his "spirit partners" are the Ojama Trio, three rather disgusting and tactless monsters that frequently annoy him. He grows fond of them over time but will never admit it under any circumstance.He gets significantly better treatment in the manga: Instead of the Ojamas, his spirit ally is the Light and Darkness Dragon, whose power even scares the Big Bad.
All Love Is Unrequited: Despite his massive (and often hilarious) crush on Asuka, the poor guy was doomed from the get-go.
Insistent Terminology: In the Japanese version, he insists that people show him respect by addressing him with the -san honorific: "Manjoume-san da" ("It's Mr. Manjoume"). This leads to his in-universe nickname of "Manjoume Thunder" when he transfers to a new school and his new classmates mistake "san da" for the Japanese pronunciation of "thunder".
Lost in Translation: His "Manjoume Thunder" nickname in the Japanese version- a nickname born from a Japanese wordplay pun- was replaced by "Let's Chazz it up!" and "The Chazz" in the dub. Unfortunately, this removes the explanation for why he starts using more lightning-based cards and symbolism after acquiring the nickname.
Obelisk Blue. Judai's designated female love interest (which, to her initial disappointment, comes to nothing) and the token shonen fanservice girl... which she hates. Kind, friendly, not-at-all proud or arrogant like most Obelisks, but has a predictably hard time in a series where she's surrounded by boys and Ho Yay.
Action Girl <—> Faux Action Girl: Zigzagged. She's considered one of the seven best duelists in Duel Academy, but she merely wins against filler opponents and has a victory in a plot-important duel only twice. However, she manages to push her opponents pretty close to defeat before having the tables turned on her and is able to hold her own against the guys (Judai, Fubuki, and Manjoume), as well as battle people that gave the rest of the cast some issues (Titan, for example). The major question is if she lives up to her hype, which, of course, YMMV.
All Love Is Unrequited: Does not reciprocate Manjoume's crush on her, and Judai does not reciprocate her crush on him.
“Well Done Son” Guy: His father runs a sake corporation (hot sauce in the dub) and Chumley wants to be a member of the dueling industry to make his father proud. He disagrees at first anyway, but the Power of Friendship changes his mind.
Daichi Misawa (Bastion Misawa)
Ra Yellow. The top student in Ra Yellow and smartest student at Duel Academia... at least before a disturbing romantic rendezvous in mid-Season 1; his shtick in Season 2 changed from being a genius to being forgotten by all the characters and ignored by the recruiting Cult.
Voiced by: Yuuki Masuda (Japanese) and Eric Stuart (English)
The Magic Poker Equation: A pointed aversion, he's one of the few characters in the Yu-Gi-Oh! universe who doesn't rely on it. He uses mathematical formulas and science to fine-tune his decks to perfection, thereby minimizing the variable of luck in his duels and making his decks very precise and strategic, and he considers what he knows about the opponent's deck before choosing one of his own six as the best choice to counter the opponent. Unfortunately most of his opponents do rely on this trope and have Plot Armor to boot.
The Worf Effect: Beyond his one win against Manjoume, despite dueling impeccably, he never wins another duel... until he joins the Society of Light during Season 2...and even those wins are only against unnamed characters.
Obelisk Blue. Sho's older brother, nicknamed the Kaiser. Originally the top student at Duel Academia who prided himself on dueling with respect and honor, before a devastating loss to Edo Phoenix prompted an unexpected and long Face Heel Turn.
Voiced by: Takeshi Maeda (Japanese) and Scotty Ray (English)Ryo Marufuji (U.S. name: Zane Truesdale), Sho's Aloof Big Brother, who goes by his nickname, the Kaiser; once the best of the best, he had a serious breakdown after losing a duel to Edo Phoenix.Season 1:
The Ace: A variation. Described as "perfect" on multiple occasions, effortlessly defeats the main character in his first on-screen duel, and is the undefeated best duelist at the Academy. Only duels three times in the season (two of them against Judai) because they couldn't figure out how to make it dramatic anymore. Not quite charming, and definitely not hammy, but he fits the bill. Sets him up for a brutalDeconstruction in Season 2.
Always Someone Better: The first to defeat Judai, who probably counts as a form of Unknown Rival, and is barely disputed as superior (at least until the Graduation Duel).
During the Phantom Demons arc, he easily destroys a villain without taking a single hit, before she forces him to make a Heroic Sacrifice for Sho. Judai very nearly loses against the same villain in the next episode.
The Magic Poker Equation: Hoo boy. Topdecks all of the cards he needs to bring out his ace monster, Cyber End Dragon, within 3 turns, tops.
Married to the Job: A borderline example; similarly to Asuka, he states that he is devoted to dueling and uninterested in relationships. Of course, this was said to a middle school Fangirl, so take that as you will.
Unexplained Recovery: In contrast to the explained revivals of the other characters, he just randomly shows up. In his case, he literally has heart failure before fading away, whereas the others simply fade away, but were really trapped in another dimension.
Fubuki Tenjoin (Atticus Rhodes)
Obelisk Blue. Asuka's older brother and Kaiser's best friend, missing for the first half of Season 1 and brought back a dangerous mystery that would not be solved until Season 4.
Informed Ability: He's considered to be one of the best duelists at Duel Academy. Despite this, he never wins a single duel on-screen. Though to be fair, two of his opponents were Judai and HellKaiser Ryo, and it's implied that he wasn't playing seriously in his duel against Asuka. Lives up to the hype in the manga though.
Judai's new rival in Season 2. By day, he's the top duelist in the Pro League and the unfortunate dupe of his manager and best friend Saiou in recruiting members for the Society of Light cult; by night, he prowls dark alleys dressed up as Duel Monsters, defeating criminals in an attempt to find the man who killed his father.
Voiced by: Akira Ishida (Japanese) and Pete Zarustica (English)
Always Someone Better: Becomes the first person in the series to defeat Ryou, and give Judai one of his few losses (though Judai later returns the favor).
Broken Ace: An extremely popular and talented individual not only in duel monsters but in a variety of professions. Yet he's overly driven by the death of his father as well as his best friend's change.
The Dulcinea Effect: For Amon's girlfriend Ekou in Season 3. This even confuses him, not just the viewers.
Shadow Archetype: Quite deliberately a contrast for Judai; uses a similar deck(Hero themed) and had similar childhood passions for his hero monsters, but Edo takes dueling far more seriously, seeing it as way of dealing justice.
Osiris Red. Initially a one-shot character with a crush on Kaiser, she returns at the end of season two and earns her way into the academy by becoming runner-up in the Genex Tournament, despite still being too young to enter the academy the normal way. Develops a major crush on Judai, to which he is predictably oblivious.
The champion of Duel Academy's west branch, who trains for duels via life-threatening high wire stunts, which he claims aide his drawing skills. Initially a pawn of Cobra, he eventually becomes a valued friend to Judai.
Badass: Put it this way — you can count on one hand the number of times Judai loses. When he duels Judai as the Supreme King, O'Brien forces a double KO, and in an earlier duel with Judai where he lost, he could have won had he gone with the second of two strategies he was considering.
Voodoo Shark: Fire-attribute cards apparently explode. This makes perfect sense to everyone and is never contested.
Jim "Crocodile" Cook
The champion of Duel Academy's south branch, who carries a crocodile on his back in a special backpack. Becomes friends with Judai and company after dueling Kenzan, and provides a nice amount of Plucky Comic Relief even in the darkest parts of the series.
Voiced by: Naoya Iwahashi (Japanese) and Tom Wayland (English)
Verbal Tic: Japanese version only - while Daitokuji-sensei often says "nya", Japanese cat meow, at the end of his sentences, other languages eliminate it altogether, and give him a German accent due to the fact he teaches alchemy.
Nice Job Breaking It, Hero: Season 3 would have gone a lot different if he hadn't brought Professor Cobra to Duel Academy, making his scheme possible. To make matters worse he leaves just as all of the students are passing out due to the Dis Bands.
Hidden Depths: Season 3 has him actual care about the students, mostly brought on by the presence of his son Martin.
Papa Wolf: But not as much as he'd like. He purposely isolates himself from Martin because showing favoritism towards a student is taboo for a teacher. (And it's the hardest thing he ever had to do, as he admits.)
Put on a Bus: Left to spend time with his son Martin, so he was absent in season 4.
Saiou's younger sister, who has ambiguous Psychic Powers og her own. Although initially appearing to be her brother's minion, her primary goal in Season 2 is to get Edo and Judai to save her brother from the evil possessing him.
The champion of Duel Academy's east branch. Initially a neutral character, he actively attempts to thwart Cobra's plans before aiding Yubel. Disappears for a considerable length of time and appears in the third alternate dimension harnessing the powers of Exodia in an attempt to rid himself of Yubel's influence.
Voiced by: Nobuya Mine (Japanese) and Darrun Dunstan (English)
A God Am I: Wishes to become the King of the alternate dimensions.
The main antagonist of season three, behind all the others. A possessive duel spirit from Judai's youth, she seeks him out due to a promise made by Judai's past life - with Judai himself has no knowledge of. Driven mad by the Light of Ruin.
Expy: Of Yami Bakura and Yami Marik. Yubel has the same hairstyle as both, a third eye like Yami Marik, gets similar bulgy veins and a Nightmare Face to the latter as well, and has just as much craziness as both before her Heel Face Turn.
Face Heel Turn: Gets corrupted by the Light of Ruin after being sent in space by Judai.
The envoy of Darkness, who demonstrates an ever-increasing number of inhuman powers - teleportation, shapeshifting, ripping holes in the dimensional fabric to duel Judai, possession and the ability to erase people from existence, to name a few.
Break the Cutie: Not nearly as much as in the anime, but it's hard on him watching his mentor go into a coma, and he briefly falls into a Heroic BSOD during his duel with Reggie, as he knows that the loser will suffer a penalty game.
Sadistic Choice: Chronos forces him to duel Sho. If he wins, Sho will be expelled, and if he loses, his deck will be confiscated. He decides to win, and it turns out that Sho's 0 on the last test, the reason he was in trouble, was not his final grade.
Screw the Money, I Have Rules!: Has to prove to his peers that he wasn't only admitted to the academy (and given the unprecedented assignment to Obelisk Blue upon entry) because of his family's wealth.
Adaptational Badass: Admittedly starts out as weak as before, but toughens up much more quickly this time around. His mistake that caused Ryo to lose faith in him was not misusing a card, but throwing a game to spare the feelings of his opponent.
Big Brother Worship: Has a bit of a case of this toward Ryo, as while the other spectators are rooting for Manjoume, he is completely convinced that Ryo will win. And he turns out to be correct.
Cute Machines: Still plays Vehicroids, but uses entirely different ones.
Take Up My Sword: Knowing he was going to fall into a coma due to a shadow game, he gave Judai his deck and jacket.
Worf Had The Flu: Judai actually manages to defeat him once, but he does so while he's not using his normal deck.
Big Damn Heroes: After Judai loses to Tragoedia when the latter is possessing Fubuki, Kuriboh saves him from the penalty game. He does it again with Light and Darkness Dragon after Tragoedia's defeat, sealing him permanently.
Undying Loyalty: To Manjoume, watching his duel with Judai, even after said owner pitched a tantrum and buried him so that Manjoume could try proving that he could duel on his own. Naturally, Manjoume came back.
The Voiceless: Actions speak well enough when you're a Dragon Spirit.
Stern Teacher: Doesn't hesitate to go hard on Judai, although typically does so in a cheerful manner.
Worf Had The Flu: She gives up a chance to win in order to try to help Koyo. By the time she's committed herself to finishing Reggie off to protect Judai, it's too late
Agent Scully: There must be a logical explanation for multiple people falling unconscious after dueling today, just like at the BattleCityTournament. There's no way it's evil sorcery like the records claim.
This is hinted at much earlier when a flashback shows the end result of what we're led to believe was a complete Curb-Stomp Battle with David Rabb biting the proverbial curb. Remember that Rabb is one of the Co-Dragons who gave Manjoume a rough time when they dueled.
Unwitting Pawn: Just like his anime counterpart with Saiou and DD, has no clue that his adoptive father and mentor is Tragoedia's puppet, or that he's giving people over to Tragoedia.
Elemental Heroes/Evil Heroes
Judai's core deck theme revolving around low-level monsters based on comic book superheroes, they can fuse together and use support cards to perform powerful combos.As part of Judai's fall to darkness in Season 3, his deck is corrupted, giving him darker alternate artworks for the base Elemental Heroes and entirely replacing their Fusions with darker Evil Hero monsters, who can only be summoned with Dark Fusion. The Evil Heroes sacrifice the flexibility of the Elemental Heroes (specifically by requiring a specific Fusion card) in exchange for more raw power in the form of stronger effects compared to their counterparts.
An archetype based on cards Judai designed as a child, they were sent into space on a time capsule and infused with cosmic energy. They consist of the six base Neo-Spacians, Elemental Hero Neos, and some other non Neo-Spacian cards that still fit the general theme/idea, like Rallis the Star Bird.
Dark Is Not Evil: Once he turns back to good he still uses the Cyberdarks. However, the only usage he makes of the Cyber Dragons while evil is as fodder to power up the Cyberdarks, so Light Is Not Good is mostly averted.
Dragons Up the Yin Yang: Played straight as can be with the Cyber Dragons and Cyberdarks representing the two halves of the symbol.
Expy: Ryo's status as an Expy of Kaiba is hard to dispute when Cyber End Dragon looks like a combination of Blue-Eyes Ultimate Dragon and Blue-Eyes Shining Dragon. By the same token, Cyberdark Dragon could be considered an Expy of Red-Eyes Black Dragon.
Meaningful Name: "Ojamashimasu" is a Japanese phrase roughly translating as "pardon me for interrupting/intruding". It's why the flavor text on the card mentions the Ojamas always butt in on things, and why their stronger cards fill up the opponent's Monster Zones.
Shout Out: Many to English literature, such as Double Dude being based on Jekyll and Hyde.
Time Master: Their effects revolve around time control, with effects relying on doing things on later turns. For example, Diamond Dude lets you discard the top card of your deck, and if it's a Spell you can activate its effect on your next turn.
Phantom Demons (Sacred Beasts)
Three powerful and dangerous cards sealed under Duel Academy - Uria, Lord of Searing Flames; Hamon, Lord of Striking Thunder; and Raviel, Lord of Phantasms.
Awesome, but Impractical: At least with the God Cards, getting three monsters onto the field was fairly feasible. But good luck summoning these guys, whose summon requirements are to tribute three Continuous Traps, three Continuous Spells, and three Fiend-type Monsters.
Awesome But Practical: On the other hand, if you set up your deck specifically around them (for example, if you run a pure Fiend Deck for Raviel)...