Yotogi no Futago: Niehime wa Futari no Ouji ni Aisareru

Synopsis

"I've always wanted to have your child", but it turns out... Hilma has honed her magical powers to become the strongest in the kingdom, in order to marry the prince of her dreams, Yuo. However, it turns out the prince actually has a twin! Now Hilma must serve the twin princes, Arm and Yuo...? (Source: Shogakukan, translated)