Kiss de Okoshite. Wake Up With The Kiss.

Synopsis

Ena is in her first year of high school and she keeps receiving confessions from weird guys. Her friend Miu jokingly says "Maybe you have a curse that forbids you to have a mutual love?" When Ena's mother decides to remarry, Ena discovers that she'll have a little brother and sister... However, the "little brother", Touma, actually is the same age as her, and he's handsome! Since they don't have a blood relationship, Touma says: "You absolutely can't fall in love with me, okay?" How will their relationship develop, now that they have become a family? (Source: Shueisha, translated)