Souta designated this man, Gremina, as the most dangerous Two Shackles Realm expert that he saw. He was stronger than the average squad leader from Athens by a lot.
His instinct as a monster was screaming. He should run away as far as possible from this man.
If Souta really couldn't handle this man, then he would run away. Using his release form at this moment would only weaken him in the next battle.
This was just a side quest. This was just the first battle, so he couldn't use his release form carelessly. He would have to fight Three, Four, or Five Shackles Realm experts when they raided the main base of the Red Matter Association.
Completing that quest was much more important than this side quest.
The release form of the fourth stage monsters was several times stronger than third stage monsters. But that cheat skill has side effects on his body, especially since he just evolved a few weeks ago.