|Race||Demon - Hydra|
|Occupation|| Tarquin's Demon|
Zacharias' Demon (former)
Obadiah's Demon (former)
He was said to have the body of a water monitor with three snake-like heads growing. Trebius was rather large, though much of his size was from his long necks, yet he was still large enough to be ridden.
Trebius has a vicious temperament to anyone who is not part of the Forsyth family. In the Inquisition he is seen licking Tarquin's wounds.
Trebius once belonged to Obadiah Forsyth who passed it down to his son Zacharias. Zacharias was apparently quite fond Trebius to which he described as his "pride and joy." Yet he, in turn, would pass it down to his son Tarquin.
Tarquin would take Trebius with him to Vocans Academy when he is sent there. He was out when Tarquin, Isadora and Sylva were exploring Corcillum. But despite that he did not intervene when Sylva was attacked and kidnapped by several men.
The next day during class Tarquin's teacher would be injured and left with Ether poisoning after she was attacked by a Shrike when she entered the Ether. Tarquin would summon Trebius to fight Fletcher and Ignatius after he scared the Shrike that he planned to capture. Though they were stopped by the arrival of Arcturus and Scipio.
Trebius would face off against Ignatius in the final tournament. Though he initially gained the upper hand, the Salamander would be able to defeat him.