Uchi ni Tomete yo ♪ ~Bitch na JK to Hame Makuri Dousei Seikatsu~

Shibata Gorou is a man in his 30s who has no girlfriend. He's just a janitor, and his life has been dull with no excitement or romance. One day, he encounters a high school girl named Sakuragi Rumina, who is known for her promiscuity at the school where Gorou works. Rumina asks Gorou to let her stay at his place, promising to make it worth his while.

[From official site]