
Minchan has already passed away in an accident when he was young, and his soul had long been gone and replaced by Seoho's soul. The curse we're talking about is the one placed by Binhwa.
I said he might be "planning" to sacrifice himself because the soul replacement inadvertently disrupted the natural order of things. This might lead to Binhwa feeling like the only way to resolve the situation and give the souls' peace is through self-sacrifice (ofc, no one's dying here but his future decision might put himself in danger in hopes of freeing Minchan). I hope you get what I mean.

I don’t think that theory about Michan death is true , didn’t the brother said he has to replace fragments by fragments the soul of michan by the soul of seoho, plus biwan after discussing with him has a dilem about letting Sappho completely come back and leaving michan disappear… so I personally don’t think that part about michan death is correct

Yes, correct, they are fragmented. However, it is already implied that the more balls he ate after killing demons, the more his original pieces gets replaced with Seoho. So yes, technically its still there but he's also been eating demon balls for so long. And this raises conflict for Bihwan as well. Why? Because he needs to choose. After all, Bihwan's whole thing in the beginning is getting seoho back.
Did he undo the curse? is he crying?? As long as this ends well I can handle the angst