Kedamono Damono(2004)

Kedamono Damono

Your typical romance story between a girl (Konatsu Narumiya) and a guy... except that this guy changes into a pervy girl! He can only change into a girl during the night. Konatsu is the manager of the boys' basketball team, has a crush on the team captain. Unfortunately, the team captain is a complete jerk. When Konatsu confides in another team member, Haruki, about her troubles, their relationship grows closer. The only problem: Haruki is a nice ordinary boy by day, but a pervy girl by night!

(Source: Tokyopop)