The plot takes a dark turn when Misaki Fujioka is diagnosed with leukemia . During an outing at a Ferris wheel, Misaki collapses, eventually passing away in the hospital.
Unlike her melancholic and detached persona in the main series, Mei is shown as a much happier and more emotional character while around her sister.
The OVA ends by bridging the gap to the first episode of the series. It shows Mei at the hospital to deliver a doll to her deceased sister's coffin, which is where she first encounters the series' protagonist, Kōichi Sakakibara , in the elevator.
It explores the relationship between the two sisters, who were separated at birth and raised as cousins. They meet in secret to spend time together, shopping and visiting an amusement park.