From MangaHelpers:
Fuwa Wataru is a high-school age boy who loves cute stuff like stuffed animals. He's at an arcade one day, trying to win a cute new stuffed bear, when bullies show up to torment him. In fleeing from them, he happens across a very special toy-catching game---one that has a naked man in it. The man calls himself "Mofu-tarou" (after the name of the stuffed bear) and insists that he is a stuffed animal. He does seem to have genuine stuffed animal ears and a tail, at least. He follows Wataru home, determined to be his new stuffed animal. Wataru's life gets even weirder as his Mumu-tan stuffed bear starts talking, and he has to figure out how to hide his new Mofu-tarou "stuffed animal."