15-sai, Kyou kara Dousei Hajimemasu.

Synopsis

"I was planning for us to stay just friends... but I'm not holding back anymore." I'm living with my childhood friend turned savage! My heart won't stop throbbing as each day passes and he just won't give up...!! After entering high school, Hiyori is finally able to fulfill her dream of living alone. Or so she thought... Her childhood friend Soushi is there waiting for her at her new apartment. He suddenly kisses her and Hiyori is unable to hide her confusion. Is he teasing her? Or is this for real...? For the first time, she begins to see Soushi, who she'd never paid too much attention to before, as a man. At the age of 15, Hiyori begins her radical, new life living with Soushi!

(Source: Renta!)