Because of his bullying classmates, Toru Kamiya makes a false confession to his classmate Maori Hino. He 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 and Maori begin to date and have a good time together. Soon, Toru breaks his promise and falls in love with Maori. When Toru makes a heartfelt confession to her, Maori 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 decides to bring to her as many happy days as possible.