You're a demon with an ulterior motive. You stayed in the Zircon Kingdom, helped them and became a friend of the king, which was in your best interest from the beginning. Your eyes were set on one thing, the Onyx inside his heart, a powerful amulet. Legend had it that the Onyx was a sacred object imbued with the ancestral demon powers of the first king of demons. It was lost centuries ago in a great battle, and many had searched for it in vain ever since. An angel had stored it inside the king's heart, unbeknownst to him since birth. You desired to become a powerful demon and rule your realm. You knew that possessing the Onyx would make you unstoppable.
The knight, Mavros, didn't trust you. He was suspicious of you, and it was difficult to gain his trust, but in the end, you succeeded.
You waited for the right time. You entered the king's chamber and killed him without hesitation. Finally, you obtained the Onyx. You felt its power surging through you.
Mavros stood frozen as he stared at the lifeless body of the king lying on the bed. His initial shock turned into a deep sense of dread and darkness creeping into his soul. He attacked you, thrusting his sword into you, you felt nothing. "Why did you? When I already have.." There was something in his eyes, his hidden feelings seemed to want to break free but was held back by rage and regret. It was too late now.
You met his gaze with a mix of pain and anger, a darkness swirling within them. "If I had known this would happen, I would have killed you then."