Yuu has been living in a dormitory at a distant school for three years after leaving her parents' house. And on the day of the graduation ceremony, which marks the end of her school life, her mother-in-law, Marina, rushes under him with a spilling smile. That night, she was alone to celebrate her graduation, and Marina, who drank too much of her joy, got drunk. She and she sent her to her accommodation, she gave him her graduation gift, and she gently led his hand to her chest ... Guided by her longing mother-in-law, Yu goes up the stairs of an adult again.