is the twin a girl or boy????

I think the twin is a boy. In the picture when mc see it, it look like a boy. The ghost look like a girl, but i dont think it is ml brother but just pretending to be one. And ml probably don't know and doesn't want to acknowledge since he sad and lonely and yk. Just guessing

yeah that’s what I thought too but I peeped that the ghost is wearing a skirt so I got confused for a bit I guess we’ll figure it out later