This is a grub theme about Chinese VOCALOID singer, Luo Tianyi.
The picture background.png looks like this:
It uses an artwork of TID and should only be used in non-commercial purposes.
The folder Tianyi includes a grub theme for 1920 by 1080 screens, and the folder Tianyi_2k includes a grub theme for 2520 by 1680 screens.
This theme can be installed like any other grub themes, the detailed guide for installing a grub theme is here