Ninin ga Shinobuden(2000)

2x2=Shinobuden

Shinobu is the only girl that goes to the secret Ninja Academy, which is presided over by a strange, yellow, ball-organism, Onsokumaru. While he knows nothing about being a ninja master, he loses no opportunity to exploit the dim but cute Shinobu. On a mission to steal all the panties from area high school girls, Shinobu meets Kaede who gets drawn into the surreal, ecchi, but fun world of Shinobu.

(Source: Anime News Network)