Killu trained with his father in the daytime, and he endured the long hours with Illumi every night. He learned to sleep with his eyes open and remember everything, learned to nap while meditating. Eventually he learned to split his mind from his Nen and rest his mind somewhat as the Nen monitored his surroundings. Memories of these periods were half-memories, incoherent and soon forgotten. An hour of sleep was a luxury, a night of it merely a dream.

Silva's lessons were about Nen and with Nen, and they were usually even interesting. He learned Zetsu quickly, as Silva thought he would, and Ren as well. He began sparring against Kalluto, with his brother forbidden to use his Hatsu. Still, Killu rarely hurt him, and he had lost to his younger brother more times than he could count. He felt that he could do better, that he must be able to... if he wasn't so tired...

Before the Hunter Exam, Illumi had trained him to endure pain; now, he was taught to inflict it. Sometimes Illumi chose himself as the target, sometimes Gon, and sometimes people who were already targets of one of the brothers.

It was small wonder, then, that in such an existence, Killua found his Hatsu almost without realizing what it was.

Illumi had finished before the dawn, an unusual occurrence in their training. It had been a particularly hard night, with Killu expected to focus Nen on an intent to cause himself pain. He had finally figured out how to do it. It was a different variant of the same technique that allowed him to sleep while using Nen - splitting his mind from his Nen, giving the Nen the order to hurt the mind, and ignoring the fear of coming pain as he had learned from Illumi over the years.

Killu was in too much pain to sleep. Rogue fragments of his own Nen ravaged his mind. Silva told me to practice forms of energy...

He gathered a strand of Nen into his hands, letting it radiate a gentle, soothing warmth.

Then Killu changed the energy back to its base Nen form, and then to electricity that flickered between his palms until he noticed the pain, several seconds later, and brought it back to Nen. Why didn't Silva mention this when he was talking about the viable forms of energy?

The first glow of dawn appeared on the horizon, and Killua started limping to the highest chamber, where he and Silva trained. There's still time. I can sleep for a few minutes after I get there.

"Show me."

The electricity passed between Killua's palms again, and Silva nodded. "Killua... this ability is not common to Transmuters. This is your Hatsu."

"No wonder it feels so powerful."

"Six days from now, you will begin training in Nen with Illumi at night, learning the capabilities and natural limitations of your Hatsu. He will no longer teach you the methods of pain. You may sleep, further your training alone, or take on work during the day. Until then, you are to learn what you can alone. I trust you to use them well."

"I... I will, Father."

Killu spent two days sleeping.

Killu ran the transformed energy across his body - usually at low levels to save himself pain - so as to be fully adjusted to the feel of his Hatsu, which conducted differently from regular electricity. He also practiced Gyo, as he did not know what his next opponent would capable of and didn't want to go blindly into a fight.

He continued his sparring sessions with Kalluto, but did not go to Illumi.

Gon remained locked in the lowest chamber, and only Illumi remembered him.

The nightly training wasn't nearly as painful as Killu had thought they would be. He was free to sleep all day afterwards, and often, he did.

When Killu went to Illumi's rooms for the night's training, he found Illumi sitting on the bed, one hand resting casually on Gon's back. Killu knew that the control he was employing would make it impossible for Gon to move at all. Still, his eyes were flaming with hatred. Illumi seemed to ignore the still body beside him as he asked, "What progress have you made in developing your Hatsu?"

Killu placed his hand on Gon's back next to Illumi's and focused on the feel of Nen. Electricity surged down his fingers. Gon's skin became red around where he had touched.

He saw the boy try to move, try to squirm away from the burning pain.

"Stronger."

Held in place by Illumi's Nen, Gon could not even scream as the searing pain burned away his skin.

"Kill."

Killu closed his eyes in order to concentrate fully on his aura. Then the electricity burned through Gon in a split second, and Killu took his hand off of the corpse's back. Illumi did the same.

Black eyes met black eyes.

"Good boy, Killu."