Takamine is a high school girl who has a lot of fun after school. One day, she meets Sakukura, a student from another school who loves to read after picking up a book she had dropped on the train. As they interact with each other in a mysterious after-school exchange through “books,” Takamine and Sakukura begin to become attracted to each other. The blue spring of girls who develop a nameless relationship that is neither friendship nor love.

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好きなことが見つけられず、放課後を持て余す女子高生・高峯。ある日、電車内で落とした本を取り違えたことから読書好きの他校の生徒・咲倉と出会う。「本」を介した放課後のみの不思議な交流の中、高峯と咲倉はお互いに惹かれ始めていき──。友情でも恋愛でもない、ふたりだけの名前のない関係性を育む少女たちの青い春──。