Jun Igarashi, who attends Seikyo Gakuen, is an ordinary school, and is struggling with love problems like an ordinary student. However, the object of his love interest is not a typical one, but Keiko Nagumo, who is as far in age as his father and son! She has no romantic rivals, but the ring that shines on her left ring finger is blocking her thoughts. One day, Jun's conversation with his classmate Sayi, who was seated next to him after changing classes, gives him a boost...