「あのとき助けていただいたモンスター娘です。」異世界おっさん教師 突然のモテ期に困惑する raw 第01-03巻 [Ano toki tasukete itadaita monsutamusume desu isekai ossan kyoshi totsuzen no moteki ni konwaku suru vol 01-03]

Some 20 years have passed since the protagonist was summoned to another world and retired from the army. He is still single in his 40s and lives as a low-ranking professor, until one day, an elite 'monster girl' transfers into his class.