Ano Toki Tasukete Itadaita Monster Musume DesuThe Girl Monster I Saved; The Girl Monster I Saved.; あのとき助けていただいたモンスター娘です。; Ano Toki Tasukete Itadaita Monster Musume Desu.

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.