Just Mai and Edwin's relationship. It only happened due to fans pushing for it and the chemistry they had.
How much Mai changed for the better thanks to being with Edwin; having someone who loves her not because of her looks or her dueling skills but because of who she is allowed her to finally break free of the walls she placed around her heart
Edwin flat out admitting that he finds Mai far sexier dressed down and casual than her glammed up
Word of God stating that because of Edwin there is simply NO WAY this Mai would ever fall into the depression that lead her to joining Doma.
The fact that Edwin and Mai are portrayed as a couple in a healthy relationship. Their bickering is always mild and playful, they take time to discuss their feelings, and they are utterly supportive of one another.
Duelist Kingdom
Kipling Chaos giving Edwin his deck and entry into Duelist Kingdom. Even though Edwin (privately) admits the deck sucks it is still a touching Passing the Torch moment.
Mako, without second thought, diving off the cruise ship to save Joey and Yugi.
Edwin deciding to break canon for the first time by getting Weevil's room key. His reason? To help warm Joey and Yugi up.
Yugi, Joey, and Edwin forming an alliance, agreeing not to challenge each other until the finals.
Alto for being the only duelist (other than Renard) to treat Edwin with respect and accept his defeat with grace.
During the tag duel against Pani K Mai has become completely broken... until Edwin begins to sing, making a fool of himself yes but also getting her to see that it isn't hopeless. When he brings down the Castle of Dark Illusions Mai is screaming and cheering, her confidence restored.
Edwin going full Rage Mode on Pani K for what he did to Mai.
Mai giving Edwin a kiss after the Duel.
When Yami Bakura begins to strangle Edwin after their Shadow Game Selene makes her appearance known for the first time, protecting him and making clear to the Spirit that he will NEVER harm her beloved again.
Tea helping calm down a terrified Edwin when he wakes up thinking the Spirit is still strangling him.
Edwin attempting to get Joey the money for Serenity's operation. Though Joey's ego ruins it Edwin was still working to help her
Pegasus, upon learning WHY Joey crashed the tournament, decides no matter what happens he will pay for the operation if he has to.
Battle City
When Jean Claude Magnum shows up Edwin doesn't even bat an eye; he knows Mai is with him and he isn't worried.
Him supporting Mai to take down the actor herself.
Edwin and Tea claiming each other as brother and sister. Later entries show them now having a playful sibling relationship.
Serenity and Joey FINALLY sitting down and discussing their issues, realizing that they can't hide things or focus on the past anymore.
The fact that Yugi's perfect world would be one where all his friends are happy. Crosses over with Tearjerker with many of them.
Joey's dad is sober and is a loving parent.
Tristan's dad is supportive of him and lets him live without the worry he has to take over the family business
Tea's dad was never a corrupt cop and she never dealt with that trauma.
Seto and Yugi met at a tournament and became good friends.
Cecelia Pegasus is still alive.
Edwin and Mai are married and expecting their first child
For Yugi his grandpa in this world is his dad.
Chapter 99, "The Death of the Guardian Devil"
Edwin finding himself in limbo and, at long last, reuniting with the spirit of his deceased mother.
The reveal that Edwin didn't end up in Yu-Gi-Oh! because of Selene; his mother sent him there because she knew they needed someone to help them, calling Edwin "her miracle"
While Edwin can't go with her to Heaven his mother is clear that Heaven is DESPERATE for him to arrive. He can't go though...
...because he is needed on Earth, as shown by the ghostly forms of Tea, Mai, Renard, Yuri, Yugi, Joey, Tristan and everyone else Edwin has touched dragging him back to the land of the living.
As the dead collectors of the many different Death Gods show up to collect Edwin's soul who should stand in their way but Brom, defying his own nature to inform them that they will not be claiming Edwin that day.
Joey preparing to sacrifice his life to save his friends from Ishizu's new Obelisk-infused form, thinking that he'll at least see Edwin soon.
Seto comforting Serenity and Mokuba, the former breaking down sobbing on his shoulder, when they learn Edwin has died.
Edwin returning to the world of the living.
When he opens his eyes rather than the black and gold energy he gained when he tapped into the Key his eyes are now Gold and White as he turns the Shadow Realm into a glorious blue sky.
Edwin's return has him purify the Millennium Key, freeing the souls of the dead thieves that were killed to make it. The Millennium Key now belongs to Edwin and Edwin alone, finally fully free of Zorc's taint.
Later chapters reveal that the spirits of Kul Elna have asked Edwin to save the other souls still trapped in the Millennium Items. Edwin agrees at once.
The Spirits of the Thieves briefly possessing Edwin to tell Ishizu that they forgive her... and Edwin will save her too.
Tea seeing Edwin's mother, who quietly begs her to love his son; Tea assures her they will.
While Edwin later declares he is no longer The Guardian Devil the title won't be forgotten: The Pharaoh claims it for himself, to honor Edwin.
The final reveal that Edwin was left with one last gift from his mother: a pair of angelic wings tattooed on his back, to remind him he is no devil... he is an angel.
Chapter 100, "Dancing In the Moonlight"
After all the death, danger, and drama the fact that Edwin and Mai go all out to just have a fun duel.
Edwin's brother Josiah getting to watch his brother duel with his own friends in their world.
In Josiah's world Serenity is Tea's best friend.
Gozaburo was a loving stepfather to Seto and Mokuba in this world, resulting in Seto being more like Canon Mai in that he is a rival who is also a firm friend of the group.
The reveal in the flashforward to the GX Era that Edwin and Mai get married.
The Slifer Dorm under Edwin run of the school is VASTLY improved.
Based on the last names Edwin brought much of the Kaiba Crew to the school to be teachers.
Followed by the bigger reveal that in the 5Ds era not only are Mai and Edwin alive but they've adopted Akiza.
Considering that in canon Akiza's parents feared her psychic powers and didn't have the greatest relationship with her seeing her and Edwin together as loving daughter/father is so wonderful.
The Chaos Contract
NONE is just a pile of tearjerker due to his origins (he is a Chaos trapped in a Pokemon World Timeloop; his second go through he became Missing No and accidentally nuked the entire world) and the fact that he has lived millions of years all alone. But thanks to Slash (the latest self insert in that world) he has several heartwarming moments:
NONE willingly went with Wyatt to study the world outside of their reality in hopes of finding a way to free Slash. He didn't even care if it meant him being imprisoned forever.
Slash telling him that they escape together or remain trapped together.
When Wyatt gives Slash a small cut it is enough to have NONE break free, moving instantly to protect his best friend.
NONE revealing that thanks to them being outside of their universe he can FINALLY use his powers to turn Slash back into an adult woman, rather that being trapped in a trans body.
Slash breaking down in tears at being herself again
When NONE freaks out, thinking he upset her, Slash tries to explain, asking if he ever cried because he was happy. NONE states once: when she became his friend.
Spin Offs
While the overall premise of Edwin in Hell is nightmare fuel and tear jerker, the fact that Dedwin (Demon Edwin) while holding Angel Dust's contract due to tricking Valentino into selling him his soul, says that he's only still holding the contract till he can be sure Angel won't squeel and tell Alastor and Charlie what he's done and what his plans are and that if Angel proves that he can do so without an incentive. That he's perfectly fine with releasing the Porn Stars soul back to him.
When Kaiba carelessly tells the Department heads that Edwin's dead, Aria the youngest and someone who Edwin treats like a little sister breaks down in tears the other Department heads moving quickly to try and comfort her while they process themselves. Kaiba then harshly tells her to shut up only to run into Moose the head of the Janitorial department who threatens him if he see's Kaiba again that day, the other Department heads also grabbing weapons to help, Kaiba wisely choses to withdraw as his company comes together to morn their friend.
When Dedwin suggests art therapy everyone is surprisingly for it, yes while Charlie is accidentally depressing, Angel just made porn and Dedwin is using this as a chance to gain more power, Vaggie and Sir Pentious actually seem to have gotten something out of the experience and Dedwin gifts the new Millennium Eye he made to Charlie after seeing how much she liked it.
While in canon they haven't been seen onscreen together or mentioned each other, in chapter 5 we get to see Asmodeus and Beelzebub interacting with Bee acting like Ozzie's younger sister teasing him about being right no one would care about his and Fizz's relationship and helping him plan out their first official date.
