Faust is absolutely a huge fan of Sanrio. There is legit no discussion. His favorite would be Cinnamoroll or maybe the Twin Stars. It's even better if it's both.
Also, another headcanon. You remember in one of Auron's audios where he mentioned that he used to shop at Hot Topic?
Faust used to shop at Claire's. Stfu, it's true. We all know it is. I will be mad if that shit is NOT canon. (Not really Im just being silly, but come on it has to be true.)