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Erebus, Vheslia's father, was an open-minded man when it came to other races. As a man that worked in a shop, he always had to be welcoming of any customer if he didn't wanted to lose potential money, so he always had the open-mindedness to be welcoming of any person as long as they had a penny and the interest of buying something he produced.
He came from a small family of alchemists after all, to make a living they sold their products, and for that reason they had to be welcoming of any person, since he was a kid that they always taught him these things.
So he was naturally open-minded of different people than demons, and even within demons there were many races of appearances and more, they were all different and unique in their own ways, some more hardy than others, some more delicate, others more sensitive, he had to be able to get used to every person and try to discern what they want or not.
Check "The Protagnist's Sister Is Actually the Strongest"!