Board Thread:Anime/Game Discussion/@comment-8851503-20190414110237/@comment-26540901-20200305200135

KoichiSa wrote: I don't if I'm the only one to think like this, but... I think Diavolo and Doppio are not two different personalities of the same person. Rather they are two different souls residing in the same body. It might sound weird but as we can see, after Doppio's(also Diavolo's) and Bucciarati's souls were switched, Doppio remained in Bucciarati's dying body and eventually died. On the other hand, Diavolo left the body of Bucciarati.I think that's only possible if they're separate souls. Although it's possible that what everyone else say(they're actually split personalities) is true. So I respect what you guys think.

If that's the case, why couldn't Doppio leave Bucciarati's body as well? Diavolo being the only one who managed that only speaks further for Diavolo not being a "full" soul, rather like a parasite/devil, latching itself onto another person.