Based on the erotic game by Noesis.

An internet bulletin board called "Free Friends" is used as a dating site, where young girls' bodies are sold cheaply. Shuuji, a teacher, registers on the site to kill time. One day, a student from the school where he teaches, Yui, appears before him. Yui uses the bulletin board without knowing the meaning of posting on it, and Shuuji becomes abnormally excited by her, so he forcefully takes her virginity...? [From Part 1, Kurahashi Yui]

(Source: Parabook, translated)