In the manga, when Kaiba saves Jou from drowning. KAIBA. True he simply throws the key to the ocean and mocks him for it but it's a CMOH to see Kaiba giving a good damn about anyone besides himself and his brother, let alone his rival/petannoyance.
Manga only, during the first night of Duelist Kingdom there is a scene where Yuugi and Anzu are reminiscing about old times, and Yuugi offers to have Yami come out, convinced that he's who Anzu really wants to talk to. Anzu grabs Yuugi's hand and tells him he doesn't have to. "You're just fine the way you are." Awwww.
Yami has to rescue Yugi's soul from a Chinese shadow game called Dragon Cards. The expression on his face when Yugi's soul returns is so tender, and it's made even better by the fact that it looks like he's trying to hug Yugi's soul.
There's a blink-and-you-miss-it example early in the duelist arc in the manga. The characters are just getting used to the idea that the other Yugi is a separate person instead of just Yugi acting weird (or, Yugi is getting used to it, and his friends are looking awkward). Yugi mentions that his other self is feeling sad, and Jonouchi leans in to the Millennium Puzzle and shouts "Cheer up, Other Yugi!" Later on, Jonouchi gets some bad news about his sister and gets angsty. Yugi looks like he wants to comfort his friend, there's a scene from behind Yugi's head as he approaches... and then the Other Yugi leans in and shouts "Cheer up, Jonouchi!" It's not much, until you consider that three books ago, the Other Yugi was still setting people on fire for fun.
In the Monster World arc in the manga, Bakura resisting his Yami self in order to help Yugi and friends out. "My name is Ryou Bakura. You will not hurt my friends." Not only that, but how Yugi gets transferred into his RPG figure. At this point, Jonouchi, Anzu, and Honda have all had their souls removed and only Yugi is left. He actually requests Yami Bakura to do so with him as well, for two reason: one, because he feels it's only right that if his friends are forced to risk themselves than he should as well, and two, so Yami Yugi's soul will take over and take his place. And remember, at this point Yugi has just finally become aware of his Other Self, and hasn't even had a conversation with him yet. That's just how much Yugi has come to trust him now.
The Kaiba brothers' reunion at the end of Duelist Kingdom is a very heartwarming scene in the anime but even more so in the manga. In the manga, their reunion marks the first time Mokuba sees his brother out of the coma Yugi's "Mind Crush" put him in months earlier, and it also marks the completion of Kaiba's shattered heart.
Yu-Gi-Oh! Duel Monsters
Yu-Gi-Oh! Duel Monsters
After Yugi wins Joey's Red-Eyes Black Dragon back from the Rare Hunter and Joey tells him to keep it.
Mai giving Joey her admittance card so he can enter the duel after Bandit Keith stole his.
Yugi giving Joey the three million prize money for his sister's operation after finally defeating Pegasus.
Mako's sullen acceptance of his loss to Jounouchi (and by association, his father's disappearance), where he just barely holds back from crying and smiles, congratulating Jounouchi on his win.
Yugi's friends block Pegasus's mind reading, after Yugi collapses. You can see Tristan's spirit holding Yugi's in his arms.
The end of Yugi's duel with the possessed Joey at the pier. There have been plenty of CMoH's in the series history, but only one was so heartwarming that LittleKuriboh was unable to make fun of it.
That entire episode was just one big CMOH for Yugi. The boy thrives on them.
And Serenity too, particularly at the end of the duel when her she leaps into the water after her brother and swim down to save him (bearing in mind she's recently had major eye surgery and her bandages only came off about twenty seconds ago. She held back because she wanted the first thing she saw to be her brother, dueling).
Kisara's death, not only for obvious reasons but because that whole arc gives a whole new perspective to Kaiba's connection to his Blue-Eyes White Dragon. Until of course you consider that present day Kaiba considers BEWD his personal BFG of Duel Monsters domination, first and foremost. Kaiba's outright denial of his emotional connection to the past is downright hearbreaking at times, for this reason most of all. Notably, Word of God has explictly stated that the relationship between Seto and Kisara was meant to define the bond between Kaiba and his Blue Eyes.
Episode 52, when Yami tells Yugi that he has no memories of who he used to be. Yugi starts getting a little freaked out about it all, until Yami tells him that he doesn't care who he was -he just wants to stay with Yugi.
Yugi: Me too. Forever. I will give you all of my memories.
Just as heartwarming in the dub too, even though 4kids changed it around.
Yugi: But what if I... fail again? (near tears) How do I know I won't lose you? (silence; Yami holds Yugi's hands) Yami: I believe in you, Yugi.
Another big one for Yugi is the episode before when the Puzzle has been stolen, chained to a wall, and broken into pieces and now the whole building is on fire. Yugi refuses to abandon Yami and the Puzzle and stays in the burning building to complete the Puzzle and try to free it from the chains. Even when he passes out he still protectively clutches the Puzzle and refuses to let go.
Kaiba's smile at the end of his duel with Noa (Virtual Nightmare arc) as his brother rushes to him, now free from Noa's Mind Control.
Also, when he's trying to break Mokuba's mind control, Kaiba's expression whenever he draws cards from his deck, hoping that it will be the Blue-Eyes is heart wrenching. It's probably the only time he trembles in fear and desperation. It would be downright tear jerker were he not such a jerk.
It's a downright tear-jerker either way, whether he's a jerk or not. No, BECAUSE he is one: it proves that Kaiba, the same guy who has in the past done anything to win and not given a damn what he does to achieve his win, seeming downright heartless, really does love his little brother.
Upon arrival in ancient Egypt Yami is deeply confused. He still has no memories of his former life, and wonders if the people around him are his friends or merely his servants. Immediately afterward Mahaad comes up because he was concerned about Yami's safety, and leds him away. Not a minute later, Yami is full-on glomped by Mana. As Yami watches the two argue, the look on his face says that his question's been very thoroughly answered.
Hell, can we just say that any scene where Yugi and his Other Self/Pharaoh Atem interact is a Crowning Moment of Heartwarming? The devotiontheyhaveforeach other is truly d'awww inducing.
During the Virtual Nightmare Arc, as Yugi's running to find Anzu, he can hear her calling his name for help, and thinks he's not really the one she's calling, that he knows very well that she wants his other self. But when he finds her and she regains consciousness in his arms, she throws her arms around him and cries that she knew he would come to save her. She was thinking of him all along!
In the duel against Dartz, Dartz reduces Yami's lifepoints to zero, but he saves himself with Relay Soul. He summons Dark Magician Girl, and cannot lose until she is destroyed. Yami says that their lives are now connected, and he will protect her. His speech sounds like a love confession.
After Yugi defeats Raphael's Dreadscythe, at first it seems like Raphael is still consumed by darkness, as he goes right back to dueling. But then, he gives up all of his Life Points to bring back the monsters he had sacrificed to give Dreadscythe power. He was willing to give up his own soul to the Oricalchos to save his monsters. Then, instead of having his soul taken, the ghosts of Raphael's family appear, along with Guardian Eatos, and let him know that they never left him, and never gave up on him.
And then, Raphael smiles, and it is just so sweet because this is the first time that he's actually felt happiness after losing his family.
In a flashback to Ancient Egypt, Mahaad gets bitten by a snake. Atem immediately rushes to him and tries to suck the venom out. Mahaad is shocked and asks him to stop, as it is improper for the Prince to be doing such a thing for a servant. Atem replies that he doesn't care about such things, he has been bitten by a snake and he's going to save him. Mahaad was amazed by his kindness and swore to always protect him, realizing he would make a most worthy pharaoh.
When the Ishtar family is reunited after Battle City. At this point, Rishid, the adopted brother who was never accepted by their father as one of them, begins to tear up. Sob.
Marik: Can our family still live? Can it live... out of the dark...? Ishizu: Yes! The three of us are Tomb Guardians! No matter where we live, that will not change! We are family! As long as we have that bond, we can overcome any obstacle.
After learning about Yugi's defeat to Raphael, we see Kaiba state that this has given him yet another reason to take down Doma. He and Yugi may not be friends, but it says something about the level of respect he has for his rival to take Yugi's defeat so personally.
In the final arc of the anime, with everybody else down, and Zorc approaching the city, who steps up, putting himself between the Pharoah, Priest Seto, the capital, and an oncoming God of Evil? Our Seto Kaiba and his Blue-Eyes Ultimate Dragon. Seeing Kaiba, who has for so long refused to accept his connection to the past, or give a damn about anybody other than himself and his little brother putting his life on the line to save thousands of people he has never met is a Crowning Moment of Awesome & Heartwarming.
When Yugi is in a funk after Yami nearly killed Kaiba before the Duelist Kingdom finals, he's too distracted to duel Mai. She takes on a tough love approach. When Joey thinks she's trying to psyche him out, Mai points out that she is not: The reason Joey was able to make it to the finals at all was because he had the courage to stand up and fight with everything she had. Deep down, Mai was scared, and relied on mind-games and psyche-outs because she was afraid to admit to herself she wasn't all that. And when she did, she became better. Then, she turns to Yugi.
Mai: How about you, Yugi? Have you faced your fears?
At the end of the Battle City arc, Mai is about to leave town, Joey catches up to her and tries to, very awkwardly say goodbye. Mai points out that he doesn't have to say anything mushy. What he did protecting her from Ra said enough and made all the difference.
Leon Wilson or rather, von Schroder, when confronted by his brother giving him an illegal card and hacking it in play, goes through a minor Heroic BSOD, and immediately tries to destroy the card to play an honorable duel. When that doesn't work, he tries to forfeit. He wanted to fight Yugi, but never to cheat.
Yu-Gi-Oh! card game
Yu-Gi-Oh! card game
In July of 2011, Dan Green was in Pittsburgh for a tournament event for the card game. He ditched that event to go across town to a smaller anime convention— paying for a general attendance badge. He signed autographs and generally acted like a featured guest at that convention, one that the organizers didn't even know was there until two days after the con.
Tyler the Great Warrior: A one-of-a-kind, custom card given to a 14-year-old boy who could've died of embryonal sarcoma if not for a skilled doctor. Even better, he got a VIP tour of the 4Kids Yu-Gi-Oh facility.