Download Tengen Toppa Gurren Lagann.7z.

Open/Extract the .7z archive. You can use 7-Zip to do this.

Create a Skins folder in the root of your flashcart’s SD card.

Inside the 7z archive, you will find a folder called Tengen Toppa Gurren Lagann.

From this folder, copy Tengen Toppa Gurren Lagann.skn to the Skins folder on your SD.

Place the SD card back into your cart, and launch Moonshell 2.

In Moonshell 2, navigate to the Skins folder and press A on Tengen Toppa Gurren Lagann.skn to apply the theme.