As Zeref spoke his mind flashed back to that day. That terrible, horrible day when he'd finally learned the weight a single life had. All his life he had the power to hurt and kill people as he wished, but from that day onward everything had changed, shifted so that he still had the power but held no control over it. Now every life he took brought him pain because he was forced to remember her and the way the light escaped from her eyes while he was helpless to do anything more than watch. Watch as the only person who had ever meant anything to him was killed. The resulting catastrophe from that day onward was the worst his magic had ever instilled on the world.
"Zeref?" The dark wizard glanced over at the small mage, a small smile already playing at the corner of his mouth at the sound of her voice. "Do you understand?"
He was silent for a few moments, taking her in: the hopeful look in her eyes and the way her beautiful blonde hair flowed in the wind. He wanted nothing more than to say yes he did, that he understood why life was so precious, but honestly he couldn't wrap his mind around it. And as much as he wanted to tell the girl that she had opened his eyes and his mind, he could not bring himself to lie to her. She was the only one who had taken him in despite all the evil and cruel things he had done and as odd as it was…he was thankful to her. The chaos he craved seemed to be inconsequential in her presence. She was the one bright point in a lifetime of blood and death. For those reasons he could not bring himself to wrong her in anyway, which meant that he was incapable of lying to her either.
"I am sorry, but no." Her bright green eyes darkened and her entire body seemed to shrink in on itself. Without having to ask, Zeref knew what she was feeling: she had failed. She was unable to complete this task of turning him into a kind and good person. For all her intelligence and cunning and wonderfully creative manipulating this one monumental task had finally brought all of her previous success to an end. She had failed.
It pained the young man to see the girl so dejected and miserable. It was all the more painful to know that he had caused her to feel that way. Lifting his arm, he began to reach out for her, wishing to comfort her in anyway possible, but at the last second pulled back. Emotions themselves were strange to him and he was unsure how his power would react to human touch. He'd always killed anyone who'd crossed his path whether by mistake or intention, but he could not remember the last time he had actually touched another person. She was the closest anyone had ever gotten to him without being killed and he still marveled at her capability to have done so. Looking at her you would not expect such a tiny girl to be the leader of such a powerful guild and posses such power as she did. In many respects she was his equal, but most of all she was his polar opposite. In every way that he was wrong she was right. It was those two recollections that caused him to drop his hand inches from her face. He was tainted and had no right to touch something so pure.
She however, seemed to have other ideas. On seeing his hand began to drop, she acted without thinking and grabbed it for herself. The effect was instantaneous, a jolt went through his entire body from where her skin touched his and in his panic, his magic escaped his control. "Zeref," she began, but was cut off as a ball of pure darkness burst grew from where their hands were connected and encased her entire being.
"No!" Zeref screamed, desperately trying to recede the power, but it was too late. Moments later, the darkness vanished and his eyes saw the very thing he had wished to never see. The once bright and vivacious girl was motionless beside him, her lively eyes were blank and emotionless; his hand still clasped tightly onto hers.
His entire body screamed in pain and agony at what he had done. Never had he wanted to hurt this one precious girl. Never had he even dreamed of it, but here he was having killed the one person he'd wanted to protect. He screamed in agony, this had been what she had been trying to teach him. This was what it meant to take a life. It meant agony and his entire body seized up at the wrongness of such an act. Immediately, another jolt traveled down his body and without any control Zeref felt another wave of magic burst from him.
The effect was immediate, every living thing around him was suddenly black and very dead. The few people unfortunate enough to be caught in the blast were lifeless on the pavement. Horrified, Zeref felt a second wave of agony and sadness rush through him. He was an abomination to the world.
Zeref cried for the first time that day, gripping the once beautiful girl to his chest, a circle of death surrounding him, and whispered into her deaf ears, "I understand now, Mavis."