Fitness Fun is an exercise-themed rhythm game starring D3 Publisher's virtual idol Riho Futaba. Riho is putting on a special concerts for the 5th anniversary of her debut, and her manager has asked her to do dance aerobics training to perfect her rhythm.

During each song, a cursor scrolls across a set of four bars with notes arranged on them in time with the music. The player must move the cursor to as many notes as possible, and press the button on the controller in time with the music to dance along. Play well, and Riho will stay with the rhythm and earn points, but play poorly and she will start to get out of breath. If too many wrong notes are played, the song will be failed and end early.

Extra songs and costumes can be unlocked by beating preset scores in the Lesson mode. There are a total of 12 songs and 14 costumes to unlock. It is also possible to save replays of performances to watch later without the note bar obscuring the view of Riho.