Canon amelioration is kind of a fic hobby of mine. When canon kills off or otherwise gets rid of a character I want to write more with, I try to find some way of bringing them back. I like to make it at least marginally plausible.
The ending of the Yuugi-ou manga makes this harder than usual. Not only is everything wrapped up, but it’s wrapped up in such a way that to change it will reverse some wonderful and necessary character development, which is anathema to me.
But I think I may have found a way.
So, at the end of the manga Atem moves on to the afterlife and Yuugi grows up and stands on his own strength. I don't want to mess with any of that.
But what if Atem could come back later?
Let us consider Atem's situation. The Ancient Egyptian concept of the after-life was a lot like life-life. Kings still kinged, clerks still clerked and farmers still farmed--kind of a raw deal for the lower class unless their families could afford to bury a substitute with them, to do the actual work. Atem, though, is a king, so let us assume that he went on having lots of games/duels with Set and probably lots of sex, too, because hey why not?
So one 'morning' Set observes that Atem seems to be brooding, and what's up? And Atem says it's his partner, and probably waxes poetic about Yuugi and all the friends he made as Yuugi's companion-self. Set probably snorts a lot and says if Atem's missing his consort so much maybe he should go be the boy's guardian spirit, kind of like Shadi/Hasan. This would, incidentally, have the advantage of Atem being solid some of the time. Indeed, Set probably offers to lend his magic to the purpose, though only because he's tired of dueling someone who's not all there, and not for anything soppy like friendship or love, and they're all clear about that, right?
So off Atem goes, back to the living world to be Yuugi's guardian in all sorts of ways. By now, I expect Yuugi is about nineteen, probably a world-class duelist and either dating or married to Anzu. Maybe they're based in New York while Anzu is finishing at the School of American Ballet. Enter Atem and cue tearful reunions and exclamations about how far Yuugi and Anzu have both come on their own strength. Threesome all the way!
Or, possibly, moresome, because you know as soon as Seto gets wind of Atem being back around he'll just about pounce on him for matches as often as possible.
And all sorts of good stuff can follow from there.