[Kusayarou] Assassination Classroom MC – Kayano & Hayami & Yada: Pleasure Tentacles Infiltrate the Cells [English]

Holy fucking crap you're right that's the one! Thank you so much for making me relive the memory.

@Santedtra Don't know any doujin like that, but there is one extra chapter from Souma that depicted Erina cooking for a bunch of relevant female main characters from Jump at that time, which include characters you said. Probably because it's Souma so you think it is a doujin.

This reminds me. Wasn't there a crossover doujin with Bitch-sensei, Erina, Chika from World Trigger, and a buncha other shounen female characters? I vaguely recall reading something like that in my youth but I can't find it now ☹️