By buying it you directly support the development of Saint Kotar and you get what follows below.

It's here: https://store.steampowered.com/app/1350040/Saint_Kotar_Supporter_Pack/

By buying it you get: 5 location-wallpapers in 4k, 10 concept arts in 4k, 7 official soundtracks from the game, the "print your own" Yellow Mask, and a printable t-shirt template (exclusive "Saint Kotar Effigy" design).

https://store.steampowered.com/app/1350040/Saint_Kotar_Supporter_Pack/