Yarichin no Ore ga Boukan ni Osowareteta Otonashii Classmate (Kyonyuu) wo Tasukete Kuou to Shitara Gyaku ni Kyokon Futanari Chinpo Sokuochi Shita Toki no Hanashi

A guy with swagger thought he was being a big hero to his quiet classmate when she was groped in public, but she turned out to be a carnivore d*ck chick in no need of rescue. She flipped him around and f*cked him up the ass! (Source: DLsite) Official English Translation.