Abaddon

Abaddon’s appearance is quite... disturbing. He is pale, and he have noticeable eye bags because he doesn't sleep.
Demons don't need to sleep, but it might feel good to take a little nap. His hair is dark brown, shoulder-height and messy at the ends.
His eyes are blue, but when he shows strong or wild emotions it turns red momentarily.
He wears a dark green doublet with white cuffs at the end of the sleeves. The front of the doublet have small gold buttons and is held together by a dark-brown belt with a gold buckle.
He wears brown shorts, white large socks, and black leather shoes. Underneath his doublet, he wears a white shirt.

Despite his ten thousand years, Abaddon is sometimes childish, but also weird and serious. He is easily distracted, vengeful, and prone to violent or weird mood swings. He is narcissistic, believing himself to still be superior to humans despite being an inmortal demon trapped in a child's body. He ignores rules or restrictions that are placed on him. He is prone to tunnel vision, focusing on a single task or concept to the point of obsession.
Abaddon displays feral tendencies, likely a result of living in the wild for so long before Esther's uncle saved and adopted him.
He is also very ignorant of modern technology, and is completely unable to comprehend it. Abaddon is scared of pure salt, this because he is a demon and demons can't cross salt lines and will get burned if they do. Sometimes he would throw tantrums.

The hotel Undervale is where Abaddon and his 'family' Esther, her mother Katherine, and her brother Ben lives. The hotel is old and antique, and it almost doesn't have guests.