This was a lot of fun, in a way that broke my brain! I think displaying the last pressed key seems reasonable (especially if you need to get up from the keyboard from the middle of the level) but I might make it tied to a button in the UI since there's definitely a zen experience to tracing your hand along the keys once you get the hang of it. There was a really fun moment where I realized you kind of want to move your keys to match your position on screen as much as possible, and it got a lot more intuitive after that. Great job on this!