It sounds like you're referring to — likely a version of the popular rhythm/puzzle game Katana ZERO or a similarly styled "unblocked" game (often hosted on sites like unblocked games 77 , 66 , etc., for school networks).
If you're saying "good piece" — I agree that Katana ZERO is a fantastic game. Its tight gameplay, synthwave soundtrack, and time-manipulation mechanics make it a standout indie title. However, if "unblocked.kat" refers to a specific clone or flash-style game, I'd need more context. unblocked.kat