With the steady pace they are going through the Supernatural territory, Rex and the others arrived at the place where Gistella recommended after a couple of days' journey. It was a tedious process as they mainly try to avoid confronting any Supernatural.
Rex was able to match King Baralt and Queen Catsha, but he doesn't let that get in his head.
Although fighting the two ninth-rank realm Supernaturals at the same time proves that he's stronger even without the Dual King Mark. Generally, due to receiving the powerful ability from King Baralt, he knows that his enemies are not just the two of them.
It was also thanks to King John that Azzen doesn't join in the fight.
Ultimate defeat awaits him if he was forced to fight any more than King Baralt and Queen Catsha. Even without the disturbance from Azzen, killing one of them is a hard task as their life force is just too much to be killed easily.