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In the AnimeEdit
Ayu Tsukimiya is introduced as a girl running from a Taiyaki salesmen when she collides with Yuichi Aizawa, the protagonist of Kanon, in the shopping district. Yuichi and Ayu become fast friends after she meets him several more times in the shopping district, and Ayu helps him remember that they first met and became friends during Yuichi's last stay in the city seven years previous. A focus in Ayu's storyline is that she is constantly searching for something she has lost, but she does not even remember what it is, which troubles her greatly. Yuichi plays an active role in helping her try to find the item with no initial success. Shortly after Yuichi and Ayu become involved in an intimate relationship, Ayu remembers what happened in the past and disappears without a trace.
Seven years before the onset of the story, Yuichi first met Ayu in almost exactly the same place as where they collided at the beginning of Kanon. Ayu was crying at the time due to the recent death of her mother, and in an effort to make her feel better, Yuichi bought her taiyaki, which in turn became her favorite food. They met up several more times over the winter school break, and one day Yuichi obtained a small angel doll from a claw vending machine and gave it to Ayu. Yuichi stipulated that he would grant any three wishes she wished on the doll within his limited power. Her first wish was for Yuichi to never forget her. Yuichi took Ayu into the nearby forest to a clearing with a large tree in its center.
There, Ayu made her second wish that they could go to school together. Due to this, they decided to make this tree their own private "school" with special stipulations such as no homework or tests, and taiyaki is served for lunch everyday. Afterwards, Ayu decided to bury the doll in a jar near the forest. On the last day of winter break, while Yuichi and Ayu were attending their "school", Ayu was sitting up in the tree when a strong gust of wind came and knocked her out of it, causing her to land on her head and fall unconscious. This accident is what caused the young Yuichi to suppress his memories of his childhood.
After Yuichi remembers what happened in the past, he assumes Ayu died, which causes him to become depressed. During this time, Yuichi remembers the doll that Ayu buried, and gathers his friends to go find it. Once he finds and repairs it, he goes to the now cut-down tree in the forest clearing until Ayu appears again. They have a tearful reunion where Yuichi reminds her of the angel doll, and that she still has one more wish left. Ayu suggests that she might wish for Yuichi to not remember her at all, and move on. After they embrace, Ayu simply vanishes again. Later, Yuichi learns from Akiko that Ayu did not die, and had been in the hospital for seven years in a coma, making her an ikiryō. Ayu miraculously wakes up from her coma and the two are shown out in town about to go back to Yuichi's house.