The Lust of Angels.

Saori, a school girl, is molested on the notorious "molester train" of the Hanagawa line and rescued by another school girl who witnesses the act. The girl who rescues her turned out to be a new student of the same high school Saori attends. The mysterious new student Yuriko is rumoured to be a "parent killer". Yuriko then leads Saori and her friends to hunt molesters.