My Stepmother and Stepsisters Aren't Wicked manga volume 4 features story and art by Otsuji.

Miya, an illegitimate child taken in by the prominent Kounokura main family, never had much of a formal education before arriving at her new home. Her stepmother and stepsisters feel she has learned all she can within the confines of their estate though and enroll her in a prestigious all-girls academy. Surrounded by the daughters of society’s most elite families, Miya can’t help but feel out of place. And when the queen bee of the entire school singles her out just to tell her she’s not up to snuff, Miya definitely feels the pressure! Will she be able to prove herself to her classmates?!