Seraphina had faced life and death several times.
When she possessed Sofia, she knew right away that William was no ordinary man, and she even harbored some feelings for him at one point.
However, the more she interacted with William, the more she realized how inscrutable he was.
It's natural for women to be attracted to powerful men, but just how powerful William was had become a mystery.
Judging from the powers William had displayed, Seraphina found it hard to estimate, but based on the strength of Amy's two masters...
She could guess that William was likely on the same level as two high-ranking god-kings.
It was very possible that William was even more powerful than those two high-ranking god-kings.
Otherwise, how could he have both high-ranking god-kings teaching Amy at the same time?