11年前の5月13日に予想外の時間移動をしてしまった、阿良々木暦と忍野忍。暦は「明日の母の日に、母親に会いに行こうとして交通事故に遭い、幽霊となってしまう運命」の八九寺真宵を助けようと思い付く。
Part 1 of 4. August 20th. It's the last day of the summer vacation. Koyomi met Yotsugi Ononogi again when he was looking for Mayoi to give her big backpack she forgot at his house. After he got home, Shinobu points out that Koyomi hasn't do his homework yet. He wants her to go back to yesterday with her power.
