Keep in mimd I am not a mobile dev but do have experience with hair and cloth and crappy hardwarw. From what I understand vertex operations are very expensive on mobile hardware.
That said I had a look at Fire Emblem Fates on youtube. I don’t think they are simulating in game. The cloth animations are always the same for each character animation and they unnaturally return to idle between turns. Simulating cloth, even simple cloth with spring solvers can be an expensive proposition. I’m fairly certain the animation is canned.
So there’s three ways off the top of my head to do this considering the cloth doesn’t need to interact with anything in the game other than the character it is attached to.
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Simulate the cloth in your 3D app. Bake out the geomtry use it as frames or morph/blend targets in game. You’ll get nice fluid cloth, but it can make for a much larger asset depending on the vertex density of the cloth and number of frames. Also, can be expensive to compute in game if your hardware is slow with vertex calculatuons.
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Rig the cloth and animate it just like the rest of your character. This will be the cheapest way to go, and you can use simple rigid body physics and spring solvers in your 3D app to help the animation look more natural. You’d set keys on the bones at intervals to translate that simulation to simple joint animation for your game.
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full cloth sim in your 3D package, bake frames, rig the cloth rest pose, match bones to the baked frames, keyframe bones to export simple joint animation to game. Depending on your level of expertise and choice of 3D package this method can be simple or extremely labor intensive. It may produce better visual results than option 2 while be as inexpensive at run time.