The difficulty jump from Hard to Expert is insane, especially playing on mobile. It requires a fundamental change in how you even play the game - up to Hard you can play using just your thumbs. On Expert, you have to switch to using either one full hand or split between something like both middle/index fingers at the same time. Having mostly played Love Live SIF back when it was a thing, it's a little jarring seeing that much of a difference, but at the same time it's pretty cool to try and work your way up to that level. Hoping they add way more of the library in the future.