Nobody talks about this one. A guy finds a girl who sings, and the entire show is built around what that moment does to him, not romance, not plot, just the raw fact that her voice changes everything. The music is the story. It's twelve minutes that understand something most shows spend entire seasons getting wrong: that sometimes you don't need a reason to care about someone, you just need to hear them. The ONA format means there's no filler, no compromise. Pure emotional clarity.
Kanojo wa Utau, Dakara Boku wa. is a 2020 music ONA.