Boku ni Harem Sefure ga Dekita Riyuu

Story

Three gals are crazy about Nanashi, a gloomy guy in class! Nanashi, who has no immunity to girls, is tormented and aroused by the innocent and unconscious seduction of the gals! Then the three gals forcefully come to Nanashi's house... Nanashi is secretly teased along with the gals' dirty talk. Eventually, their conversation turns to sex... Nanashi explodes with excitement, saying, "I want to try it!" The gals attack him! His body and mind fall into the sexfriend experience that begins with a 4P!

Synopsis via AniList (English).