Matsunaga Yoshihiro has visited The Dragonfly Coast, a remote sea beach, seeking solitude, but met a girl, a kindred soul of him, instead. Their summer ended in the twinkling of an eye and the girl has dissapeared. "I will wait for you by the sea", were her last words.

7 years later Yoshihiro being a tour conductor is accompanying a group of students and teachers on their 'Summer School', half educational half recreational trip to The Dragonfly Coast. Cherishing a vague hope he steps on that land again, and the ever blue sea is awaiting him.