I have no real headcanons for this scenario, but my favorite thing to see people do when playing Miitopia is to make the Reborn Dark Curse be a perfect copy of the Main Hero, in a sort of twist of fate where the latter is giving up half of their soul so that the former can live again with a face others will trust and respect.
I also just see that type of scenario acting as a counter for the trope of the "We're not so different, you and I" bad guy monologue, if that makes sense.
When the Miitopia Switch Port comes out tomorrow (as of this writing, I might already be playing it), that is 100% what I intend to do.
bruuuhh this is dark but its awesome, oml-
tbh ive never seen this done before, but props to you and those that follow this headcanon, its one of the best ive seen in terms of reviving the reborn-