Even though Seraphelis had become his soul servant card, Ethan could only use her power when he activated the servant's aggressive mode.
There was a big level gap between his other soul servants and Seraphelis, one that was hard to ignore.
Ethan wanted to know if that difference also affected the duration of the aggressive mode and its cooldown.
But trying it out right now would be pointless if he was just doing it out of curiosity. The best option was to wait for an actual combat moment, then activate Seraphelis alone in aggressive mode.
By making Sera—who was technically a fragment of a soul—his soul servant, it was Ethan's way of protecting her completely.
A soul servant only died or became inactive if their master died.
In this case, Seraphelis would die or deactivate if Ethan died.
That made things easier for him. He didn't need to protect both himself and Sera separately—if he stayed alive, she would be fine.
