Haruhito Ishimoto, a second-year high school student, lost his parents in an accident. He now lives with his twenty-four-year-old older sister, Konoka, who works to support him. Haruhito harbors romantic feelings for Konoka, and after learning they are not blood relatives, he is conflicted about whether to confess, despite feeling it might be wrong.

Meanwhile, Konoka also harbors feelings for Haruhito that are more than just brotherly. Despite feeling it's wrong, she finds herself unable to suppress her feelings for him...