Imouto no Meshitsukai kara Kaihousareta Watashi wa Koushaku-ke no Kateikyoushi ni narimashita

[title](https://www.cmoa.jp/title/263731/) Colette had always wanted to be a knight but lost her place in the Kiels family when she defeated her older brother in a swordfight. Treated like a servant by her younger sister, she is eventually caught up in a scheme and kicked out of the house. She moves to a small town in a neighboring country together with Renri, the butler of the Kiels family who accompanied her. But when she finds herself in trouble, she ends up working at the mansion of the stoic Duke of Lacheret, the deputy commander of the knight order. There, she learns about a different side of him, who is known as the Iron Mask, and Colette gradually falls in love with him.