Main character is a seemingly ordinary university student who lives with his sister. But in fact he has only memory of recent events after he miraculously survived the car accident that took lives of his parents. He often sees a dream where an unknown woman "Chisa" calls him by an unfamiliar name. That woman strangely reminds him his sister. One summer hero gets invited to work as assistant to professor villa together with other students. However, it's not the professor who greets him, but a mysterious woman...