Theatrhythm: Final Fantasy soundtracks onto iTunes today, each comprising songs from a particular mode of the 3DS and iOS game. There's a soundtrack each for the game's Event, Field, and Battle gameplay modes, each one priced $8.97, along with one for the Chaos Shrine mode, priced $9.99.
The game aside, what these essentially represent are Final Fantasy 1-13 compilations, with the Event, Field, and Battle soundtracks each including one song in its original version from each of the first 13 main FF games. Take the Battle one, which includes a piece of battle music from each game, though not always the main one; FF7 and FF10 are represented by "One Winged Angel" and "Fight With Seymour," for example.
The Field soundtrack comprises a mixture of the games' main themes and songs you hear in particular locations, while the Event soundtrack picks some of the iconic songs (mostly) from the 13 games, like "Celes's Theme" from FF6 and "Waltz for the Moon" from FF8.
Finally, the 15 songs of the Chaos Shrine are much more scattered. Nonetheless, there are some excellent ones in there such as the melancholy "Zanarkand" of FF10 and the rousing "Blinded by Light" of FF13.