Nobara and Kotori are twins. Ever since their dad died saving Nobara, the twins have been switching identities! One day, Kotori ,as Nobara, was killed waiting for Nobara to switch back! Ever since, Nobara, as Kotori, has been living as her sister for her mom, because she knows that her mom needs "Kotori" the most. Only her boyfriend, Yuuwa, knows that "Kotori" is Nobara, but is willing to keep the secret.