Toshoshitsu No Kanojo Seiso Na Kimi Ga Ochiru M New Online

"Toshoshitsu no Kanojo" or "The Library Girl" is a Japanese manga and anime series that revolves around the daily life of a high school girl named Sakura Yoshida, who works part-time in a school library. However, I believe you are referring to a specific fan-made or doujinshi work titled "Toshoshitsu no Kanojo, Seiso na Kimi ga Ochiru made" which roughly translates to "The Library Girl, Until You Fall into a Slump".