Yugi Muto wasn't the only character who got stuck in the madness. These character originate from Yu-Gi-Oh! as a whole.
Seto Kaiba
Yugi's rival. The only reason he gets involved is because no one gets to fight Yugi head-on except him. Unfortunately, this narrow-minded thinking causes more trouble than good.
- Badass Boast: Gives one to the Slasher during their duel.Kaiba: A piece of filth like you has no right to touch us duelists! Listen well, garbage; I will not accept anything less but your complete and utter defeat!
- Brainwashed and Crazy: By Yugi to kill Kairi under a Loophole Abuse (ie, no member of the Darkness Proxy can harm her) in The Friendship Asylum. Thankfully, Princess Peach purifies him before it's too late.
- The Caretaker: In the final story, he's tasked by Princess Peach to tend to Perry the Parasol. Despite the oddness of this, he takes this role seriously and is horrified when the Upheaval in Act III causes Perry to be stuck in Limbo without any hope of escape.
- Curb-Stomp Battle: Utterly obliterates the Slasher when the latter duels him.
- Deadpan Snarker: It's not Kaiba without his trademark snark, now is it?
- Decon-Recon Switch: His rivalry with Yugi. The Friendship Asylum deconstructs this mindset, as it made him vulnerable to getting mind controlled. It's reconstructed in Through Darkness and Mirrors, since, in his own way, it also means that he's willing to give Yugi encouragement (In his own way, mind you) and rise up against the stigma the Darkness Proxy are going through.
- Duels Decide Everything: An Invoked Trope. After the Friendship Asylum, Kaiba has learned how to use the Quantum Cube to initiate this.
- Heroic BSoD: Kaiba of all gods get into this in Through Darkness and Mirrors when he finds his hands empty because Perry the Parasol slipped out of his hands during the upheaval in Limbo, thus the boy is trapped without hope of escape.
- Light Is Not Good: Wields the legendary Blue Eyes White Dragons...and he is not a nice person.
- Little "No": He can only utter this at the end of Act III in Through Darkness and Mirrors all while staring at his empty hands. Why is this important? He was taking care of Perry the Parasol as his team traversed Limbo, but Alt!Gentaro's temper tantrum caused an upheaval, with Kaiba thrown back to the Pantheon and Perry stuck in Limbo without anyone to save him.
- Nice Job Breaking It, Hero:
- Going after Yugi in The Friendship Asylum unleashed the Disaster dominoes that would eventually be the Undead Uprising.
- Evaporating the Lake of Reincarnation in Through Darkness and Mirrors meant one less portal to Limbo and its healing waters unavailable in Act IV.
- Odd Friendship: With Princess Peach, since the princess trust him enough to take care of Perry for her while she's on vacation.
- The Only One Allowed to Defeat You: His usual dynamic with Yugi, but after the Asylum was dealt with, resulting in Yugi being in a Heroic BSoD, Kaiba's actually willing to defend the guy! ...If only so that when they duel again, Yugi would be worth defeating.
- This way of thinking actually caused more trouble than good in The Friendship Asylum since it gave Yugi a chance to brainwash him, nearly kill Kairi, cause Sora to go insane, unleash the Undead Uprising and traumatize various gods in the process thus pavinf the way foe the final story.
- Papa Wolf: Sota, you may be crazy, but using Kaiba's brother as a bargaining chip was practically suicidal.
- Pet the Dog: He may think Sota is a nuisance, but he does have him uploaded into his Duel Disk before he fades away, thus making Limbo unable to kill him and prolong his life a bit longer.
- Teeth-Clenched Teamwork: With Joey (usual rivalry), Dean Ambrose (because it's Ambrose's fault that Kaiba almost killed Kairi), and Sota (Because the guy has No Social Skills and makes too many innuendos for his own good).
- There's No Kill like Overkill: His "battle" with Sota was to put it this way, absolute overkill.
Mokuba Kaiba
Younger brother and herald of Seto Kaiba who appears in the final story as, what else, bait.
- Audience Surrogate: Since he arrives in the last story, he's being used for the audience to follow along the events that happened in the previous two stories.
- Big Brother Worship: He's petitioning to become god of this trope when Through Darkness and Mirrors starts and has this seat by the epilogue.
- Designated Victim: He's captured by Guardian Muneca in the final story and left on a boat in the Lake of Reincarnation. Unlike most examples, he gets out with a few mental scars on him.
- Foil: To Nanako; they're both quasideities (Nanako even had a temple in the same sub-house Mokuba is in prior to Family Dynamics) who love their older brothers and are just so cute. The major difference is that Nanako is much more proactive and has fighting capabilities while Mokuba gets captured and nearly sinks into the Lake of Reincarnation. Also, Nanako gets brainwashed by XANA while Mokuba — who was brainwashed once — escapes it.
- Heroic BSoD: Has a minor one when he learned just what his brother went through (and indirectly caused) in The Friendship Asylum.
- This Is Unforgivable!: Says this to Dean Ambrose in the epilogue after Ambrose performs a Face–Heel Turn (seeing as Ambrose was the one who helped Mokuba ascend in the first place).
Joey Wheeler/Katsuya Jounochi
Yugi's best friend who arrives in the final story in utter disbelief that Yugi could be a monster.
- Badass Normal: No magic, no money, just wits, luck and being a Determinator are his tools of the trade.
- Berserk Button: Gets pissed when gods accuse Yugi of being a monster and even more pissed when he learns from the Guardians of the Galaxy just what Yugi had done months before he ascended. And then even MORE pissed when he sees The Slasher seemingly try to get Yugi to relapse.
- Brainwashed and Crazy: Fused with the Lord of the Red armor in his duel against the Slasher, he gets brainwashed by the Slasher's Guardian Muneca monster, and then Obsolete Soul Crusher to make sure the control is complete. This sets Yugi's Berserk Button off.
- Dark Is Not Evil: Utilizes a Red Eyes Black Dragon deck but has no evil bone in his body.
- Dub Name Change: His dub name is used by non-Japanese gods to overall familiarity with it.
- Fighting from the Inside: The entire reason the Slasher was forced to summon another Dark Synchro Monster was to avert this, as Muneca's control wasn't complete.
- Foil: To Gentaro, believe it or not. Delinquent-like characters who are in to friendship and have a connection to Yugi, and while Joey is willing to fight to save Yugi, Gentaro (rather Sota) wants to crush Yugi to pieces only because Yugi's unknowingly holding a powerful artifact in him. Plus, Joey is shown to be downright nervous upon seeing the variety of horrors in Limbo, while Gentaro (as both Mala Suerte and Sota) are unfazed by it all.
- Locked Out of the Loop:
Word of God states that he arrived around October, and didn't know that Yugi got corrupted into a complete dick until Through Darkness and Mirrors started (which is in December). This is lampshaded by Peter Quill, who questions where Joey has been for the past few months to not know his best friend was an a-hole for about a week. Dark Magician later fills him in as Lord of the Red. - Playing with Fire: Red-Eyes Black Flare Dragon is covered in fire, his Red-Eyes monsters all attack with fire, and Lord of the Red is a FIRE-Attribute Ritual Monster.
- Sinister Scythe: When brainwashed (see above)
- Teeth-Clenched Teamwork: With Kaiba (as usual) and The Slasher/Sota (for being a creep, although the latter apologized for his word choice).
- Tranquil Fury: He doesn't get to act on it, but he tells Atem, in a deathly quiet voice, to leave the finishing blow on the Slasher to him.
- This Is Unforgivable!: Says this word for word when Through Darkness and Mirrors starts up, swearing that he'll punch whomever is behind this as payback for what they did to his best friend.
- You Are Not Alone: Reminds Yugi of this along with Téa.
Téa Gardener/Anzu Masaki
Yugi's childhood friend who consoles the boy after the trauma and harassment he gets.
- Dub Name Change: Like Joey above.
- The Heart: Of the entire group.
- Non-Action Guy: She stays back while everyone else ventures Limbo. Although she does help since she has a flashdrive from Elena detailing what will become Operation: Inside Out.
- The Smurfette Principle: Not counting Yubel, she's the sole female character from the YGO series to get involved.
Jaden Yuki/Yubel
The second YGO protagonist and his partner, who is hoping to see if the darkness he uses can stop the one in Limbo.
- Ascended Extra: Appeared in one scene in The Friendship Asylum, he's now on the front lines in stopping Limbo.
- Dark Is Not Evil: Jaden is the reincarnation of the Supreme King of Darkness who fights off against the evil Light of Destruction.
- My Significance Sense Is Tingling: He's able to tell if the Darkness has possessed or corrupted someone, as well as identify that the cards Bandit Keith is using are not a product of the Darkness, but rather a power derived from the YGO-verse as a whole.
Bandit Keith
A cut-throat duelist who gets sucked into Limbo early into the story, returning with a horrifying vengeance in Act IV.
- The Alcoholic: At the start of the story, he's plumb drunk.
- Big Bad Wannabe: His possession and usage of the three Wicked Gods seems to set him up to be a very deadly opponent...only for him to lose to Yugi and give the good guys the edge they need to keep the Darkness back.
- Chekhov's Gunman: Is mentioned to have fallen into one of the Limbo portals early on, and is seen being approached by a mysterious figure. He finally reappears in Act IV as a pawn of the Darkness, and the mysterious figure is revealed to be Akato.
- Demonic Possession: Courtesy of the Wicked Gods, the Darkness, and Noxicron.
- Many Spirits Inside of One: As discussed in Demonic Possession, he's possessed by five of these. However, since the Jashin work for Noxicron in his universe, the latter is mostly in control.
- Pure Is Not Good: Whilst under the control of the Wicked Gods, he's filled only with the desire for revenge on Yugi so that he's a viable candidate for the Keystone of Limbo.
- Sanity Slippage: Suffers this in a manner very similar to his role in R!. By the time he finds Yugi, he's been broken down into a mass of pure revenge.
- Unwitting Pawn: He's actually one to Akato, who decided to test a card that one of Akato's superiors, who goes by the name of Noxicron, is planning to use later down the line.
- Walking Spoiler: Why on earth does this guy have so many spoiler tags, I wonder?
- Whole-Plot Reference: His role was derived from the R! Spin-Off manga, and his possessed design takes cues from his Rare Hunter days in the anime.
