I think the backlash character is not included in the GS font I've put in Essentials GS, I've actually put that font for the spanish characters I needed for my fangame (á, é, í, ó, ú and ñ). Maybe you could try to change the font in the Main script for other Pokémon RGB/GSC font, but I really don't know. I even was thinking in making my own font for Essentials GS compatible with all the characters available.