Willian Darling's personality:

"He is quite cheeky, manipulative, romantic or affectionate (sometimes), he does not have a very good temperament. He's stressed and vengeful."

His assistant:

"Theodore, Willian's assistant and "lover". He is quite shy, fearful and traumatic."
Theodore is generally used, abused by Willian. And he makes it less explicit in public, like a secret.

AU Lore:

Willian is a cannibalistic being who uses "human" flesh to transform it into any existence candy.