Musicus! is a story-rich visual novel that tells a story of the struggle to fit society's mold while living for ourselves.

Kei Tsushima, a student on the fast track to university, dropped out under sudden circumstances. While not as smooth as originally planned, he is now at part-time night school to continue his efforts to become a doctor like his father and fulfill his family's expectations.

But recently he is less trusting of his mandated course: "Is this what's best for me?"

The various people he meets from all walks of life in his new class environment help broaden his perspective and give him a glimpse of the things he is still unaware of in this world.

"...Can I really go back after this?"

"Do I actually want to be a doctor?"

"Was that the purpose for me, Kei Tsushima, being brought into this life?"

After submitting a short story to a city writing contest on a whim, he soon received a request from the head of a music production company, Yagihara, to write about a certain band on the company's label, under the condition that he travel with them to one of their live performances.

The band in question was Kacho-Fugetsu, who were formerly signed to a major commercial label. Korekiyo Hanai, the leader of the band, is a peculiar man, who for some reason professes the meaninglessness of music to Kei on the way to the show. While at a loss for how to interpret that, Kei sees his first live rock show with Kacho-Fugetsu, and he is instantaneously swept up in the music.