Living in the shadow of his talented younger sister, Kyousuke Kosaka conducts a normal lifestyle until he accidentally finds out that she hides a secret. In addition to being smart, pretty, and popular; Kirino Kosaka is also an obsessive consumer of anime and eroge (adult computer games). What will Kyousuke do? Will this tear their already rocky relationship apart or bring them closer together?

Kyousuke brings Kirino home from America where she attended a special track & field camp. Surrounded by her friends, Kirino gradually gets her life back to normal. In stark contrast to her friends is Kyousuke, who is unhappy with Kirino's attitude towards him. She has been ignoring him since she came home, as if their relationship had gone back to how it had been a year earlier.