My Roommate Isn't From This World (Pre-Serialization) - Ch. 50

[MangaDex]

 

[brndndss]

now hes the one spying

 

[Aishwarya]

One-Man Hide And Seek is a game where you prepare a stuffed toy to be possessed by a ghost, play hide and seek with it and then destroy the toy. Here's a good explanation of how it goes.

Since he doesn't see the girl most of the time (only at night I guess?) maybe he wanted to try and see if she would possess the toy?