In my story.
The Warrior who can use powerful magic call "Magician Killer".
It is a big threat for the magician.
Magician killer can kill Magician easy when they close when the magician.
Defensive magic can not stop them.

To stop their attacks is Sword of the Magician work.
Sword of the Magic is combination of magic and sword.
It is mostly used for defense.
They can prevent the hostile Magician killer assassinate magician.
But they use expensive weapons.
The ability of different users.
They need different weapons.
So most of them are mercenaries.