Larvous is the second born in first generation of werewolves. After several years witches perfected the transformation potion, needing test subjects they used these potions on Hellhounds. This transformation magic became infused with their DNA as years went on, allowing a new species to rise. Everett is part of the first generation of full blood werewolves to exist. To make sure Werewolves stayed loyal to their owners just like Hellhounds, Witches also binded them with a spell, which is marked on their foreheads. This keeps them from hiding amongst wild Hellhounds and from disobeying their masters. Despite this spell however, if their magic is strong enough, they could theoretically break the spell themselves.
While Everett desperately fights against his Hellhound half, Larvous embraces it, allowing him to fully master his third stage.