You are Riku, the son of a diplomat who has relocated from Japan several times, most recently living in the United States. His estranged mother's recent unexpected illness forces Riku and his father to move back to Japan to care for a younger sister he does not remember, and finish his high school education in the town where he met his first friend as a small child.
As high school students together, you, she, your sister and the class rep make fast friends and have adventures together through the year in this slice of life eroge.