@tomtom78 yea but whatever it is, it's an alien. It doesn't seem like it identifies with a particular gender either, it's clearly not human. Even the hair, he said it's not like normal hair and something seems to be keeping the hair grouped up. So I don't blame MC for being like that, he's probably torn between fear and unknown of what this entity is and what it may do to him given time, as well as also feeling sorry for it because it does seem pitiful.
@tomtom78 Based on Chapter 3, it looks like he lives with his grandmother. He'd probably feel like he'd have to tell grandma the full circumstances if he was going to try to persuade her to let Mogu stay.
Given the levels of trust Grandma appears to have in him in this chapter ("Yes, the girl you brought home can sleep in your room."), he probably doesn't want to do anything to jeopardize that.