Responses
I think it's more that mugo was originally 1 entity/personality, but then something bad happened causing him to split into 3(?): sir mugo, monster, and asshole. Now sonething abt the mc is causing the lines to blur between them. That said, mungo's personalities view themselves as separate entities, so if they assimilate, theoretically it would mean 2 would disappear
so, as far as i know, the kind mugo is the original one, he was there before the other 2/3
while mean mugo and cute mugo met alone, they were both going to die so that's why theh made a deal and became one quite kind mugo, BUT before the asimilation was completed, cute mugo was made to promise he'll remain in the shadows until the others say so
now, due to our mc treating each one of them as a separate beings, they're slowly breaking down what kept them together to begin with, which is dangerous because it means only 1 of the 3/4 souls habitating the body will survive