15-sai, Kyou kara Dousei Hajimemasu.

Synopsis

"I planned on us staying friends forever... but I'm done holding back." I have to live with my childhood friend who's turned into a beast! My heart pounds every single day, and he just won't stop coming at me...!! When Hiyori enters high school, she finally gets to achieve her dream of living by herself. Or so she believed... But her childhood friend Soushi is already waiting at her new apartment. Out of nowhere, he kisses her, and Hiyori can't hide her confusion. Is he just messing with her? Or is he being serious...? For the first time, she starts seeing Soushi—someone she never really paid much attention to—as a man. At age 15, Hiyori begins her drastic new life, cohabitating with Soushi!