ドメスティックな彼女 (Series) favorite_border

Volume 1 Synopsis: Natsuki, a high school student, harbors an unrequited love for Hina — a bright, popular teacher. But after a chance encounter at a mixer, he ends up getting involved with Rui, a girl with a dark, mysterious air. Then, out of nowhere, his father announces he's getting remarried — and the woman's children turn out to be none other than Hina and Rui!? A wild new life together is about to begin!