Ninin ga shinobuden (2004)

Shinobu is a naive ninja-in-training. In order to test her ninja abilites, she must steal the panties of all the high school girls. The first house she stops at is the abode of one Kaede Shiranui, who happens to catch Shinobu in the act. Kaeda is the voice of reason and the two girls become quick friends, despite a round yellow ball-thing who claims to be a ninja master and tries to get in the way of their friendship.