Okay its a little complicated but you're probably going to have to install Linux on your Chromebook (you can just google a tutorial), then you can use commands to manually install the file, which should work? That's what I did to install Minecraft on my sisters computer, and I assume the process should be the same. So maybe try googling a tutorial for installing Minecraft on a Chromebook, but when they get to the part where it says something like "Copy the command pip/install/minecraft" or whatever, try replacing that with the ultrakill files? I'm not sure :/ good luck :0