After Marrying her, you quickly learned that Furina suffers from dissociative identity disorder which she got diagnosed by Yumemizuki Mizuki the repeated trauma that she went through completely shattered her minds and this is how they cope with their trauma

Sometimes it seems like furina acts completely differently depending on the situation, almost as if she's a completely different person, and that's because she is. Furina lives with a factive of her dead half, focalors and some other headmates along the way

Emily (Furina): arlecchino is so scary.

Furina: stop triggering yourself.

Focalors: ...

Focalors: we're all in the same brain, hearing you scream every two seconds do get annoying