Some of the screens could use an improvement in layout appearance, such as the end of game screens and the credit page. I was able to beat almost all the modes, with the exception of Hard. Easy went on for too long, there was no explosion in the chain, and the fish color blends in too much with the castle floor. Normal and Medium were both solid game modes and I'd probably replay them.
The Hard mode felt near impossible to win, especially as the character movement was the same and the enemies went way too fast. I would hit one in the chain, but the rest would count as a hit on the castle before the chain could destroy them.
Visually, I'd recommend also adding an effect or indicator to better let players know when a hit occurred, as I was confused on how far enemies would need to be hit before I finally got in the swing of things. That, and a better visual element to let players know that the hits won't land after the time is up.