Quick answer — Hajime Hyakkoku worked on K-ON!: The Movie (Music), Ace of the Diamond act II (Music), Ace of the Diamond act II -Second Season- (Music) and 7 more anime.
Hajime Hyakkoku worked on K-ON!: The Movie (Music), Ace of the Diamond act II (Music), Ace of the Diamond act II -Second Season- (Music), K-ON! Season 2: Plan! (Music), Saekano: How to Raise a Boring Girlfriend ♭ (Music), Saekano: How to Raise a Boring Girlfriend (Music), Gugure! Kokkuri-san (Music), GJ Club (Music) and 2 more.
