"Just two and a half months. Go out with me." Nanami Osaka, a high school student in Kamakura, has a secret she can't tell anyone. That is, sneaking into the "no trespassing" third music room and playing the piano after school. It was a precious time for Nanami, who has been unable to play the piano in front of others since a certain past, but one day he is found by a strange male student. Calling himself Yui, he presses for an exchange condition, "In exchange for keeping the secret"--? Kamakura, dusk, music room. A boy and girl with a secret, a special time for just the two of them begins.