Thank you! I'm really glad you enjoyed it!
The boss was definitely the part I had the most fun making. As for the J and K keys, they actually do the same thing, I added both so players can alternate between them for faster firing at max upgrade instead of using one key, It's actually a habit I picked up from playing rhythm game.
I'm still learning how to use Easel UI, so I'll definitely improve it later. Originally, I wanted to make the panel slide down for a cleaner, sleeker look, but I haven't figured that out yet.