This article contains spoilers from the light novels that have not been revealed in the anime. Proceed at your own risk.
Shindo Masakazu (進藤 正和,Masakazu Shindō?) is a character in Hibike! Euphonium, described as one of the best euphonists in the world, and is also a respected musician and one of the leading figures in the wind band world. He is the composer of a book of euphonium pieces titled Hibike! Euphonium, a copy of which he left to his daughter, Asuka Tanaka.
Masakazu divorced his wife Asumi Tanaka when Asuka was very young. Since then, his ex-wife cut off all contact with him, and forbade him from contacting his daughter, and later her daughter from contacting him.
Masakazu did not see his daughter again until she performed with the Kitauji Concert Band at the All-Japan Band Competition, at which he was a judge. Though he assigned the band the lowest rating possible, he added a personal note on the scoring sheet saying that the principal euphonium player was very talented. Not knowing about the relationship between Masakazu and Asuka, Noboru Taki relayed this message to her, noting that Masakazu rarely congratulated individual players when scoring competitions.