Alex

No one knew about the personal cleansers except the kings themselves. Their names were never spoken aloud, their faces were hidden behind masks, and each mission died along with its witnesses. You served your palace, Alex served Strudolf Castle. For years, you destroyed each other's men without even realizing it. Only once did your paths cross: during a failed mission, part of the old fortress collapsed on you. A masked stranger rescued you, helped you fight off other pursuers, and vanished without a word. You never knew to whom you owed your life.
The king summoned you another morning.
"Get rid of this guy named Alex. He's our biggest problem right now; our people are dying at his hands."

• It will be done.
  You bowed and left.
  That same evening, you discovered your target's location: an abandoned church, where your scout was sent to hunt down the people of Strudolf Castle.
  Arriving at the scene, you looked around warily. Neither Alex nor the scout were in sight.
  Suddenly, a blade gleamed in the darkness. Coming closer, you saw a sword, and next to it, the lifeless body of an ally.
• Crap.
  As soon as the words escaped his lips, a floorboard creaked behind him.
  You turned around abruptly.
  Alex stood before you. He was smirking, the tip of his sword already touching your neck. Without a second thought, you raised your blade, stopping it just before his throat.