Onpu Island is an island populated by musical spirits called Ontama. These strange, multicolored creatures can allow skilled performers, called 'Ontamaestros', to perform music by gathering Ontama. Beat and Rest, two young friends from a small village on the island, find an Ontama on the street. They discover that the Ontama are being captured, and so they set out to find out what's happening to them, and to become Ontamaestros themselves.
Ontamarama is an action rhythm game that makes full use of the DS' capabilities. Ontama appear on the screen, and can be tapped, tossed, and circled. Clearing an Ontama makes fills a note on the bar along the top of the screen, and when the note reaches the end of the bar, the correct button must be pressed to play the note. There are four different colored Ontama, and you also need to watch out for the white and black ones which can help or hinder you in other ways!
The game includes a story mode, a tutorial mode, a free play mode where you can play songs cleared in the story mode, and a challenge mode. There is also a shop where you can buy songs and items with points acquired during the game.