what the guy is doing in there...

Probably the typical situation of the characters going on a school trip, male character is taken by fellow guys, and then ends up in the girls room. To avoid getting caught either from returning awake girls or teachers he hides in the bedding of a sleeping girl.

lucky one

She knows he is there, how could she not, he is wrapped around her and she has a hand on his head.

She is probably hiding him so the other girls don't discover him there or this is some sort of cruel challenge/punishment (or both! O_O)