One of the strongest adventurers who was one of the 「Four Heroes」who had saved the kingdom — Rolf Audenitt — Witnessed, Miria, the little sister of his comrade who died a year ago, become a s*ave. As the result of his thoughtless purchase ー He ended up living under the same roof with a young girl. 「My older sister was killed by that demon.」 Meanwhile, Miria’s eyes were stained with hatred for 『Demons』who had robbed her precious family. 「….Master, I beg of you, please train me. To the extent that I can destroy the enemies.」 And then, Rolf realized the hidden potential within Miria and decided to take her as his disciple. This is the story of a s*ave girl who aims to be 『The Strongest』 and former hero adventurer who will nurturing her.