I have so many thoughts. Metaphor? Psychosis caused by black mold? Literal mold demon? With the mind of something formed 5 years ago, at that. If he is semi-real...
The notes upstairs: either he learns fast... or he accesses people's memories through invading their body, maybe? I mean, either Mould wrote that or he possessed your grandfather to do it. Worse, the first words when starting the game: "I know everything about you".
He also seems nameless, but oh so happy to be named. Demon behavior altogether, I tell you all. Very evil spirit core. I hope for Mould that he's not doomed to kill the protagonist. Even when he tries to be sweet, the fruit is poison, his touch brands your skin, you lose your sense of self. It's hardly love, but he's one sad puppy.