Theatrhythm Final Fantasy is a rhythm video game. Players take control of four Final Fantasy characters, and select a Final Fantasy game from the first Final Fantasy to Final Fantasy XIII. Each game has three stages: field, battle, and event. Each stage features different game mechanics than the others; once a stage is completed, the characters level up. The difficulty level can be changed in order to make it appealing to "beginners and rhythm masters alike". Throughout the game, players can unlock music and movie scenes. The gameplay requires players to tap on the screen in correct spots to the beat of the music playing. Within the main game section "Series Mode", there are 3 unique stage styles: Field (Overworld) Music, Battle Music, and Event (Dramatic) Music, as well as the option to play through the opening and ending themes.
Source: Wikipedia, "Theatrhythm Final Fantasy", available under the CC-BY-SA License.