It's a WebGL build? Please, can you add a Unity version so I can play on XP?
Thanks for taking the time to check out the game! Unfortunetly, it's built on Pico-8 ( http://www.lexaloffle.com/pico-8.php ) with no plans to port to Unity, sorry. However, if you buy the Pico-8 console you should be able to play it (and many other amazing games)! Could be a great investment if you are running an older PC as Pico-8 has very low system requirements.
Uh, strange.. all Pico8 games works for me, maybe your has something different? (now I've just tested others again to be sure, no issues)
Or just upgrade to a newer OS..
Now the game works, dunno why. Instead of mouse I preferred a simple key that attack in the direction where is moving at the moment of press. Maybe you can add an option like it? Hey... hands down from my XP workstation!!!! :D