17-year-old Saraka Homizu invents an infinity-shaped particle accelerator named Mugen. Meanwhile, sushi bar worker and aspiring guitarist Motokazu Watanuki takes his more confident twin brother Yoshikazu's place and attends his difficult physics classes while Yoshikazu is visiting the Phi Phi Islands in Thailand. Motozaku agrees as a means to be near his crush Shiratori, who is dating Airi, a grad student assisting with the seminar.