Rino has a cousin named Miki, who is several years older. Ever since childhood, Rino has looked up to Miki like an older sister, and gradually developed special feelings for her. Miki occasionally visits Rino's house, not merely as an excuse to have dinner with her aunt, but actually to see Rino. Their bond deepens over time, and Miki slowly opens Rino's heart. Eventually, Rino steps into a forbidden world.