Nanatsuiro Drops (2007)

Tsuwabuki is a normal student, though not very social. One day he meets a new transfer student, named Sumomo Akihime, and another girl, both the only members of the gardening club. Tsuwabuki is forced by a teacher to join this club. But then he bumps into a strange guy with dog ears, switching his drink with they guy's by mistake. Drinking it, he is turned in a stuffed animal. The teacher tells him that the only way to turn back to normal is to find the chosen girl and let her catch the seven stardrops. This girl is Sumomo, that accepts to help him, though she's not allowed to know the animal's true identity.