My Stepmom's Daughter Is My Ex: Volume 2

High school was supposed to be a fresh start-new school, new me. I should be basking in the glory of my new found popularity and placing top of my class, but I can't. That's because I have to live with my stupid ex, Mizuto Irido, who is also my little stepbrother now. For the sake of our newlywed parents, we're pretending to be best friends, but behind the scenes, we hate each other's guts and would like nothing more than to see the other crash and burn.
We once thought we were deeply in love, but that was nothing but a folly of youth-a mistake that neither of us were keen on repeating. He never really understood me, even when we were dating. Nowadays, he still acts like he knows me, but that's all it is-an act. All he saw- No, all he's ever seen has been a plain-looking girl who shared a hobby with him. If someone else who fit that description asked him out, what would stop him from saying yes?