The project's README from github.com/Thang1191/Miku-Dating-Sim-GRUB-Theme. As one markdown file: README.md.
A Hatsune Miku–themed GRUB theme, remixed from the Matrix Morpheus GRUB Theme. Art by me.

The original art files with layers can be found here (clip and psd included). If you make something out of this, be sure to credit me (and send it to me too, I'd love to see it). Thanks!
Note: pls read so you know what you're getting yourself into :P (Troubleshoot guide below!!!)
Here's a quick command to see all of your classes:
grep --color=auto "class " /boot/grub/grub.cfg
GRUB_TERMINAL_OUTPUT="console", which makes GRUB silently ignore GRUB_THEME (the theme line is never written to grub.cfg). The installer switches it to gfxterm automatically; if you installed manually, change it yourself and rerun grub2-mkconfig.git clone https://github.com/Thang1191/Miku-Dating-Sim-GRUB-Theme
cd Miku-Dating-Sim-GRUB-Theme
chmod +x install.sh
sudo ./install.sh
sudo cp -r Miku-Dating-Sim /boot/grub/themes/
Then add to /etc/default/grub (or replace the existing GRUB_THEME= line):
GRUB_THEME="/boot/grub/themes/Miku-Dating-Sim/theme.txt"
And regenerate the GRUB config:
sudo grub-mkconfig -o /boot/grub/grub.cfg
The repo only includes arch.png and windows.png. You have to look into the folder and rename arch.png to [your distro's class].png. You can find your distro's class in grub.cfg. If it's too much work, just use the install script.
sudo rm -rf /boot/grub/themes/Miku-Dating-Sim
Remove the GRUB_THEME= line from /etc/default/grub, then regenerate:
sudo grub-mkconfig -o /boot/grub/grub.cfg
The installer saves a copy of
/etc/default/grubas a.bak.<timestamp>file next to it before making changes (the path is shown at the end of the install). To fully restore your previous config, copy it back before removing theGRUB_THEME=line.