Tsukaretemasen Tsukaretemasu!

High school instructor Koushi confiscated a book about magic and accidentally summoned the tiny incubus, Marin!!! Despite being an incubus, he said that he would only have sex with someone he loves, as his small body was on the verge of disappearing?!
‘I definitely won’t be affected by this kind of hallucination!’ …He said. Yet one day, he was moved by Marin’s admirable form, and just as they kissed, Marin transformed into an attractive man?!