OH MY GOD thank you for asking
the set up is basically that humans found this unlimited energy source called "magic" and they replaced all their tech & stuff with it + combined it with humans to make what are called "gears" but this started a big war called the crusades lead by a gear. it's really just a fighting game series but there is like a lot of interdimensional space/time bullshit that goes on & gets super complex but it's really fun !