Haikei, Arishihi ni Saku Hana-tachi e

拝啓、在りし日に咲く花たちへ

Kasumi, a serious girl who has just started at an all-girls school, discovers a letter tucked into an old book she found in the library. The letter's writer yearns to have a special relationship with another girl, like how it was described in the book. (Source: Kadokawa, translated)