Buu.

[Old Zangya]

The only way I can possibly think of continuing Buu's storyline is if he either went into some huge, drawn out, warlike saga, where he would completely change, or if he went training somewhere; I'm trying to figure out a way to change his appearence. Is it possible to maybe change his appearance to one of Super Buu's forms when he absorbed Gotenks? He'd still be Mr. Buu, he'd just basically be thinner, more muscular, and have a more puffy yellow and black vest.

EDIT: But the appearance would change over time throughout the war/training.