Real no Heroine wa Irimasen!

Aramiya Seiichi is an ordinary high school... eroge otaku who's given up all hope on girls in the 3D world due to a certain incident. One day, after he bought a bunch of new materials in consequence of experiencing the frustration of a perfect eroge character turning out to be "used goods," he encounters a delinquent-like-looking girl being about to get raped by a bunch of guys. By mere chance, he rescues her.

Days later, when school starts again, it turns out to have been his classmate, Ayame, a feared delinquent girl who's got all kind of rumors about her—especially that she's "used goods." And it appears that she's set on becoming his ideal girl to make him fall for her.

(Source: Novel Updates)