Misuzu, a Japanese middle schooler who lost her mother at six, is about to turn sixteen. On the night of her birthday, a girl about her own age taps on her window. She says her name is “Yoko”—Misuzu’s mother, come through time from when she was sixteen. Misuzu wants nothing more than to see her mother again, but it’s hard to square this sixteen-year-old girl with the word “mother.” After a nostalgic tour of the house with this “mother,” Yoko makes an offer: come with her on an adventure. Misuzu doesn’t know why, but she feels like she’s supposed to go, so she half-stumbles out the door after Yoko. The two pass through a long cave and somehow cross through time again, arriving more than ten years in the future. Yoko makes a phone call, and as if it were all arranged, a married couple appears with a girl of about the same age. The girl is called Tsumugi—and this Tsumugi is the daughter Misuzu will have in the future. So the one bringing Tsumugi to meet Misuzu… is the grown-up, married Misuzu herself.