Ihata Itsuha has qualified for the prefectural swimming competition, and since the venue is near her grandfather's house, she will be staying there during the event. Her grandfather, whom she hasn't seen in a while, is kind and even prepares a birthday cake to celebrate, as the day before the competition happens to be her birthday. That night, an overwhelming drowsiness suddenly hits her and she collapses. When she wakes up, she finds herself bound inside a storehouse. Standing before her is her grandfather, wearing a strangely sinister smile...