Dumping my Yu-Gi-Oh headcanons list on ya'll because I have nothing better to do today
All my headcanons are from the Duel Monsters portion of the series, most of which are influenced by the anime and personal thoughts.
Atem has a thing for anything strawberry. Strawberry drinks, baked goods, artisan goods, you name it. If it's got strawberry, Atem will almost certainly eat it. Even as Yami, he would take over Yugi's body sometimes to enjoy strawberry flavors(Yugi thought it was silly but also was happy Yami had something he liked)
Of course, my headcanon of Kaiba treating Yugi like a second little brother after Atem departs. Seriously, Yugi becoming an unofficial Kaiba brother because of Seto's love for Atem and feeling bad that Yugi doesn't have his own big brother now is something that feeds me life.
Kaiba and Atem are 100% gay and demi, Yugi is bisexual and nonbinary(goes by he/they pronouns)
Kaiba and Atem are both intersex
Atem eventually returns through magic nonsense and everyone is overjoyed to have him back (Yugi and Kaiba especially, for their own reasons)
Yugi and Marik are a couple. I just think they're cute together. They'd eventually have a son(Kaiba helps them create their son by taking Yugi and Marik's DNA and making the baby in a tube in his lab. Because I'm absolutely certain Kaiba could do that sort of thing if he tried) and name him Atemu, after Atem. Because Yugi just loves his brother so much. (cue Uncle Atem shedding tears of joy)
Atem and Kaiba get married and Atem 100% is in charge of wedding planning cause he has better tastes than Kaiba when it comes to this sort of thing. And Atem convinces Seto to let him wear a dress for the wedding. Kaiba becomes Seto Kaiba-Sennen.
Kaiba and Atem eventually have twins, a daughter named Kaida and a son named Yami, both taking Atem's last name of Sennen.
Joey becomes a KC Security Officer because he's "A good guard dog", according to Kaiba.
Atem works graphic design for Kaiba Corp (he's a surprisingly good artist)
Yugi works at Kaiba Corp for the game development division. Sometimes he brings Atemu into the office with him, and he tries to coordinate dates where Kaida and Yami are brought in when Seto and Atem come to work so their kids can bond with each other. (Yugi wants Atemu to have a deep connection with his cousins asap.)
This is just all of my current headcanons so far, and I'll probably have more later down the line, but so far, that's all.
