I think, considering the Charisma stat in D&D is less "how much of a smooth talker you are" and more "how strong is your force of will," that GS's Charisma needs to be at least 13.

Or maybe Funimation doesn't know how D&D works.

Which wouldn't be that surprising considering they called Light Novel readers cucking perverts while having no self-awareness that they hold the rights of many of those pervy light novels adaptations (including some good ones like Index, Re:Zero and Spice and Wolf) including the one My Girlfriend is a Gal mocks AND stars Jamie Marchie (High School DxD anyone?)