Hey, thank you for playing and thank you for your feedback!
If the translation is correct then you are right there needs to be an explanation where a perfect hit is.
A perfect hit is when the arrows that fall and the arrows on the tiles overlap. A perfect hit makes a sharp "ping" sound while normal/bad hits make a dull sound. The type of hit and corresponding color is also displayed for a brief moment when you hit the arrow.
I should have made that more obvious since those small details are hard to notice while playing.