A street musician and a Miku who lost her voice find each other in Shibuya, and the movie doesn't waste time pretending this is complicated. The songs don't just underscore the story, they ARE the story, each one a small conversation between two people trying to matter to someone. If you've never played Project Sekai, the emotional setup lands anyway, but the movie assumes you know why Miku matters in the first place, which means it's built for people who already understand what it means when a synthesized voice can break your heart.
Ichika Hoshino is a high school student who performs music on the streets of modern Shibuya. In a CD shop she hears a Hatsune Miku song she has never heard before, and on the store monitor she sees Miku in an unfamiliar form. After one of Ichika's street shows, that same Miku appears on her smartphone looking downcast. Miku explains that there are people she wants to reach with her songs, but no matter how much she sings, her music does not get through to them. Having watched Ichika touch the hearts of her audiences, Miku hopes to learn from her, and the two join forces to reach listeners through music. The film is a musical drama built around this new partnership.