Boku no Watashi no Yusha Gakuぼくのわたしの勇者学 ; 吾等的勇者学 ; Boku no Watashi no Yushagaku ; Our Hero Lessons ; Our Hero Studies

It opens when a mysterious strangely dressed person who the kids mistake as a new transfer student enters a peaceful classroom. Much to their surprise he is their new homeroom teacher, among other things…