Hotaro Oreki doesn't like to do things that he considers a waste of energy. However, things start to change when he enters high school because even though he does not want to join any non-compulsory school activities, his older sister requested that he join the memberless Classic Literature Club so that it won't get abolished. Unbeknownst to him, another student, Eru Chitanda, already planned to join; but instead of being free from club obligations, Hotaro eventually joined as he is strangely unable to refuse or escape from Eru's passionate gaze of curiosity. Together with his friends Satoshi and Mayaka, they began to discuss a variety of mysteries in school that only H?tar? seems to be able to solve, including the mystery that lingered on from Eru's childhood memory.
Kumiko Oumae is looking for a new beginning at Kitauji High School, distant from most of her middle school peers. She befriends Hazuki Katou and Saphire "Midori" Kawashima and joins the Music Club with them, a past-time from her junior high days. There she continues to play euphonium and encounters Reina Kousaka, a figure from her past she didn't expect to meet again. As the club works tirelessly to achieve it's goals, the two girls awkwardly dance around each other, each wanting to know the other more.
Kumiko and her teammates have won the Kyoto regional tournament. From now on, life will be getting a lot more hectic. With the national tournament fast approaching, Kumiko's band is doubling down on practice and discipline, leaving little time for sleep or other recreational activities. The redoubled practice schedule brings Kumiko and Reina closer together, but elsewhere in the band, it seems like drama threatens to tear the group's unity apart. The ghost of the prior year's mass band exodus still haunts many of Kumiko's classmates, and with former band member Nozomi Masumi now asking to return, it seems like the grudges of the past will soon be impossible to ignore.
K?sei Arima was a piano prodigy until his mother died when he was eleven years old. The shock of losing her made him lose any interest in piano, and his life has felt monotonous ever since. Then, when he's fourteen, his childhood friend Tsubaki introduces him to her classmate Kaori, a free-spirited violinist. Her enthusiasm reignites his interest in music and in life.