Matsunaga Yoshihiro is the chaperone for a group of high-school students on a summer trip to the beach. Watching over everything is a mysterious young girl who somehow is always there at decisive moments.
The first chapter of the Refrain Blue series, tells about the recollection of Yoshihiro's past about various events of summer school, of the fate where encounter and separation are interwoven with each other, as Yoshiro and Matsunaga will pass the Toyo Gakuen and will arrive at summer school at seashore. A mysterious girl smiles as she watches Yoshiro who stands still at the seashore dusk.
The second chapter in the Refrain Blue series focuses on Nao Morisawa and the events that happened at the summer camp last year, with her and Yoshihiro Matsunaga both unable to let go of feelings of the past.
In the last chapter of the Refrain Blue series, the bond between Yoshihiro Matsunaga and Nao Morisawa grows stronger, while Yoshihiro finally finds out the identify of the mysterious girl from the first chapter.
