Kyoko has a very rare disease. Her platelets are unable to clot her blood which makes her weak and vulnerable at heart. Kyoko decided to become strong for her twin sister Ema, since their father was always away on trips due to his job. It is a big surprise to the two girls that their father is going to marry Miss Asahina; their fathers girlfriend. Thrown into the midst of things, Ema and Kyoko move into the Asahina apartment where their step brothers anxiously await them. Along the way, Kyoko learns a lot about herself and her sister as th Asahina boys push their comfort zones to their limits.