"Just a heads up, I've never thought of you as my little sister." Natsuna was raised by her mother from a young age after her father's untimely death. Her family grew exponentially at 15 years old when her mother remarried, giving her two step-brothers: newly licensed doctor Hideo and Akihide, a medical student. Though her new family's elite status was intimidating, they welcomed her with open arms. Six years later... at the airport. The three siblings see their parents off as they embark on a year-long trip to study America's E.R. system. Now, the siblings will be living together without parental supervision as well as working at the same hospital. One day, Hideo kisses Natsuna out of the blue, sending her heart on a butterfly-filled romantic roller coaster. Just then, Akihide throws his hat in the ring as well. Which of the handsome doctors will win their step-sister's love...?