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! 
 
(Source: Lune-soft, translated)

One day a virgin guy, who is unaccustomed to dealing with girls, heads to his local convenience store andunexpectedly happens upon 3 gals from his class. Finding out that he lives nearby, the gals invite themselves over and barge into his place. No sooner than later do they start rummaging around his messy room for some entertainment. And entertainment they find... In the form of erotic mags and porno flicks! Naturally, the topic of conversation proceeds on to "How does one perform fellatio?" "If you lick like this, supposedly it feels really good for the guy." one of the gals says while licking her own finger as if it were a penis. Watching this all, the virgin guy is powerless to prevent himself from getting a rock hard boner. He tries to hide it from the gals, but his efforts are in vain... 
 
(Source: DLsite) 
 
Note: It has live-action AV adaptations: HUNTB-385 (2022/10/07), HUNTB-634 (2023/08/18) and HUNTC-137 (2024/06/21).