"Ano Toki Tasukete Itadaita Monster Musume desu.": Isekai Ossan Kyoushi Totsuzen no Moteki ni Konwaku suru

After twenty long years, Washio, a teacher summoned to another world, has gone to seed and become the laughingstock of the student body... until one day, he catches the eye of a breathtakingly beautiful girl who tells him: "I'm the monster girl you once saved!" By some strange twist of fate, he's won the favor of these students who were once his monster pupils... What will happen to this past-his-prime teacher?

(Source: Yen Press)