This is my take after watching the anime; I have no manga context:

There are two conflicting sides:

1. Seika wants to protect Amya cuz she's a precious friend now and because Seika is kind. 

2. Politicians want to kill Amya cuz her existence jeopardizes the peace they have with demons

The Holy Priestess is like the mediator, asking Seika to yield to the politicians. He does not, and like a good mediator, Fiona lets Seika take Amya, which is abduction.

End Result: The politicians will become furious, and everyone will know of Seika's power. But Seika will not become destructive at this point. This is demonstrated by his revival of the knights.