Unexpectedly however, the mastermind of the entire conspiracy was her mentor - Remilia

Altairya, you have done well for this mission.

To reward you I'll show you something interesting....

An assassin who relies on her underling to eliminate her enemies so she could own the holy vessel all by herself, a madman who plans to control all human thinking..

In the end this assassin managed to defeat her mentor, saving humanity, and at the same time succeeded the Assassin Order, growing it...