So this is Vermis (Formerly Sarakuel) He is a fallen angel.
He was previously an angel who, like others, was sent to destroy Vincas.
He was one step away from death, but as he died, he acknowledged Vincas' divinity and renounced his former gods.
For this he spared him. After his fall, Vermis became Vincas' servant, his loyal fanatic.
And this is an absolute form, so to speak... a mega form.
(the hole in his stomach, by the way, is from the blow of Vincas' claws)