The first details on Theatrhythem: Final Fantasy for the 3DS have surfaced, straight from the game's official website, which introduces the story and some of the music tracks that'll be in the game.
According to the site, the story once again takes the space between Cosmos and Chaos and throws various Final Fantasy characters into it, including Lightning, Cloud, and the Warrior of Light. This space is known as "Rhythm" and there's a crystal within it that fills the world with music. Unfortunately, Chaos has broken the crystal and "“ surprise, surprise "“ it's up to the heroes to save the day!
Theatrhythm will feature stages from Final Fantasy I through XIII. Each stage has three levels, Field, Battle and Event. You can form a party of four to tackle these levels, each of which will feature different gameplay systems. On top of that, there's also a character development and item-collecting system in place.
Square Enix have yet to detail how the gameplay works, but some of the songs mentioned include Clash on the Big Bridge, One Winged Angel, At Zanarkand, The Sunleth Waterscape and more importantly, the Final Fantasy Main Theme.
If you're wondering why the art style looks exactly like Kingdom Hearts mobile, it's because the art is being handled by Monster Octopus of design group MonsterSoup, the exact same artist that worked on KH Mobile, as well as other titles like Tsukibito from SNK Playmore.