My Stepmother and Stepsisters Aren't Wicked manga volume 6 features story and art by Otsuji.

The class president elections have ended with Miya's friend Koyuki chosen as their representative. But just when Miya thinks things are about to calm down and return to normal, she learns that the student council, including its ultra-strict president Mikuriya Sadame, have set their sights on her! Not only that, but it seems eldest stepsister Marika has her own bone to pick with them! Later, the girls prepare for one of the biggest events of the school year--the annual sports festival!