Endro! - Season 1 Episode 6 One Room, 100 Square Feet, Demon Lord Included!

The Hero's teacher was the renowned Mao. She never once gave Yusha and the others special treatment and provided them with the same strict education as the rest of her students, if not stricter. While Mao took it upon herself to act the villain, hoping that she might raise them into a splendid Hero's Party, one day she learned how her students truly felt. Yes, it was on the day she fell ill that-- (Excerpt taken from "I Raised the Hero -How to Raise a Hero as Told by Their Teacher-")