She didn't know why she did it, or even how.
She only knew that he didn't deserve to die.
Lying on the floor of her room, she thought about the upcoming fight. This was going to be the first true test of her abilities. Anticipation welled up inside of her. After all, she had been told that she was the strongest one of her kind yet.
A group of Galaxy Soldiers had recently arrived about 60 miles away and several demon beasts had been sent to destroy them. They had been successful and had brought back one warrior, the strongest of the group. This was the one she was going to fight. They said that he was so strong that it was necessary to weaken him before the battle.
What would it be like, to fight tooth and claw against sword? She had fought mechanical knights and shape-shifting demon beasts before, but this was the real thing. Real life or death. The tip of her tail twitched back and forth as she gathered her experience and assembled a basic strategy. If they were going to weaken him first, then the best thing to do would be to tire him out and then deliver the final blow. Yes, this would be a good fight.
Just then, someone opened the door. She squinted against the sudden flash of light. Nightmare entered the room, his hands behind his back and his manner serious. "Get ready, 56934TWG17. I want this to be an excellent fight today. If you do well, I just might give you a real demon beast name. Keep this in mind. If you fall, I cannot resurrect you." He fell silent for a few seconds, then continued. "You'll be entering from the north door this time. Do not disappoint me. Now, if you'll excuse me, I must go prepare our... guest." With a small flourish, Nightmare turned and walked away with a brisk pace.
She stood and walked down the hallway opposite from the way her master had gone. She eyed the other passing demon beasts and the blood stains on the wall. When she came to the arena door, she nodded to the demon beast standing there and settled herself down to wait. Her tail was twitching again and her claws were tapping against the door in impatience. She was too excited to sit still. She had no doubt that she would win, but would she do well enough to receive a name and become one of the master's prize monsters?
Surely they must be ready for her by now! She was ready to burst with all the energy flowing through her. She just wanted to tear through the door and destroy whatever it was they placed in front of her. She knew that she had to be careful, but still. She decided to put her ear against the door and listen. She could hear the cheering, growling, and snarling of the attending demon beasts, but not much else. Suddenly, there came a strange sound of a kind that she didn't recognize. It elicited even more cheers from the crowd, but it was new to her. She stilled herself and thought hard. It was a sound of pain, that much she could figure out. It wasn't a growl or a hiss or any other pain sound that she was familiar with. She decided that it was a cry of pain, a sound that the master had said was good to cause.
Her curiosity aroused, she pressed herself against the door. She heard her master's voice announcing the fight. "It is now time for today's fight." He paused to let the crowd roar. "Today we test 56934TWG17's abilities against this insignificant ball of space dust. Come out now, 56934TWG17! Come defeat your first knight!" Her excitement suddenly turned to seriousness, she slowly and cautiously opened the door and stepped into the light.