16-year-old super-studier Nagi Umino, second-year student at the Meguro River Academy high school, was switched at birth. On his way to a dinner to meet his birth parents, he accidentally meets the brash, outspoken, Erika Amano, who is determined to make Nagi her fake boyfriend as she never wants to actually marry. But once Nagi makes it to dinner, he finds his parents have decided to resolve the hospital switch by conveniently having him marry the daughter his birth parents raised...who turns out to be none other than Erika herself!While out shopping with Erika one day, Hiro is suddenly and mysteriously abducted! Nagi feels he has no choice but to act, so he grabs Hiro's hand...and decides to elope?! To make things even more confusing, Nagi's long-lost childhood friend (and first love) Ai-chan is back from China, and she says she has an answer to what he asked her back then...