If Arthur's acting was good before, then the appearance of Phoenix Si was no longer an act.
The former used his body to act, while the latter used his soul to transform.
The performance of the physical body was only superficial. Only the changes in the spiritual level could stimulate the human nerves.
In Arthur's eyes, the man in black armor and silver mask revealed his cold personality and swift and brutal skills with a simple action.
He was the hellhound under the queen of the empire, and he would use his sharp claws to tear apart all obstacles in front of the queen.
To him, the vice commander of the Empire was nothing.
If the queen hadn't asked Sai to fight, no one would have suspected that he would have pierced the neck of the vice commander with a sharp knife.
