Because of his bully classmates, Toru Kamiya makes a false confession to his classmate Maori Hino. Her tells her that he likes her, but she lays out rules for him if they are to date. One of her rules is that they are not to fall in love with each other. Toru Kamiya and Maori Hino begin to date and have a good time together. Soon, Toru Kamiya breaks his promise and falls in love with Maori Hino. When Toru Kamiya makes a heartfelt confession to her, she informs him that she has a disease. When she wakes up, her disease causes her to have no memory of the day before. She keeps a diary of what happened the day before and reads it in the morning to be able to recall her memories. Toru Kamiya decides to bring to her as many happy days as possible.