Beat after beat, it continues to pulse. Hearts are likely the most complicated organ to understand in the human body. It's unpredictable to all which try to comprehend its functions, yet it sustains mortal life despite its failures. It is the harbourer of our soul, our feelings, and our courage.

Courage… how long does it last?

His breaths had become ragged and hard, his eyes trained on the undefeated enemy before him. Beads of sweat ran down his skin as he recollected his stance and slowly reassured his mind. He'd taken far too many hits, and as a result his body's movement was beginning to waver. If he continued to drag it out, he'd lose, and all hope of saving him would be naught. He couldn't allow that to happen no matter what. He was going to win; he couldn't run away, he couldn't keep dodging. He had to face him head on and attack.

Illumi had wasted no energy in his attacks, and remained completely apathetic in their battle. He tilted his head every so often to see if he had crushed his little brother more so than prearranged, but every time he stood back up. That spark of determination to save Gon had only grown stronger since he saw him, and now that it was dangerously high he counted it as a threat. Illumi would need to destroy all hope of Killua saving his friend. That was his mission, and he would see it through to the end – even if the result had his little brother loathing him for the rest of his miserable life, even if he wanted to kill him and spill Illumi's blood over every surrounding surface. This was the life of an assassin.

In that moment, the air shifted towards Killua. Illumi noticed the brief alteration in the atmosphere and silently pondered what his younger brother could have been planning. He recognized the Hunter could use Nen from his perceptibly strong aura, but what more had he learnt in the time he'd left Killua to his own accord? It was time to find out…

Jolts of energy began to wisp about Killua's body, and the air gradually became hostilely sharp with illuminating blue. It staggered, reached and extracted repeated through the atmosphere as currents of inhumanely strong electricity leaping around the Zoldyck's own form. His hair softly moved with the currents as they surrounded him, and he opened his eyes to stare at his brother. Nen transformed into electricity, and Illumi finally understood Killua's power. He was a transmuter just like their father and grandfather, and deep down this gave the eldest more reason to turn him into the perfect assassin. He was destined for great power in the family and he would make it so.

Illumi's eyes slowly widened, and a prolonged sound of grandeur escaped his mouth. He was delightfully impressed, but from the indistinguishable poker face he held, it was hard to realise. "You took advantage of your training and turned your power into that of electricity, an element that your body can handle. I'm impressed, Kil." Evidently his tone was still undeniable emotionless, but Killua knew he spoke the truth in those words.

"Mother will be proud when she finds out." He added, noticing a hesitant twitch from Killua's eye.

The sparks flew off his pale skin, and whenever Illumi thought of stepping closer it threw itself in his direction to keep the assassin from moving anywhere. This was going to be a pain, but like Killua, Illumi could bear with electricity. To what extent however was unknown to the younger Zoldyck.

"But until I return, I need to make sure you are no longer corrupted by that prying child."

"After you fail, I'm going to kill Gon."

Those words were the trigger to his switch.

Thunderous assaults of bolted electricity aimed at Illumi and destroyed the floor at his feet, forcing him to jump into the air and dodge to the side with ease. However in mere seconds it was hot on his trail and coming at full force to his side. At the very touch the power destroyed the walls and roof, breaking it with ease and leaving nothing but tracks of destruction behind. Rubble disintegrated and wood flew from the ground by the force hitting it.

Unfathomable anger ran through his veins, and by each moment passing his aura grew stronger to the point he could no longer control it subconsciously. It leaked from his body, and with it his abilities shockingly levelled up until it enclosed the whole complex. His body stood still, his eyes fuelled by unmeasured rage. That beautiful sapphire was now a dark swirl of rough ocean blue, covered in shadow by his outrageous blood thirst.

He would not allow Gon to die.

Blue lightning crashed through the maintained windows with a loud clatter, and the smell of burnt material filled the air as the sparks of Killua's power scorched all that it came in contact with. Illumi dodged out of the way from another attack, and found the gaseous air from the burning structure become a hindrance to his senses. With slight annoyance, the male narrowly avoided a large spark of energy heading his way. In seconds, he disappeared from sight as the scale of electricity hit the wall behind and utterly destroyed it. It was remarkable what Killua had accomplished by channelling his fury.

As Illumi disappeared, Killua widened his eyes and looked around the room to find it empty – and completely ruined. It was barely supporting itself from the ground up to the roof, and a mere step made the entire apartment unstable.

"Gon-!" He instantly thought of his friend and leaped across the room out into the hall. The room behind him collapsed to the ninth level below, but he ignored the crashing and ran to his friend's location. Something crossed his vision midway and the silver haired boy skid across the ground to a halt. Where had that suddenly come from? As he tried to find the source, Killua felt a stream of warm liquid run down his cheek, followed by a light sting of pain. Killua turned his head and saw four large golden needles speedily heading his way, but recognized he wasn't fast enough to evade them.

They wouldn't have been fatal, but due to their ability to change bodily structure it would have been agonizing to deal with. Something however… had dragged Killua backwards against his will, and he found himself hitting the ground as the needles missed and impaled the wall alongside him.

How did he…?

No, that wasn't his instinct that caused his body to move out of the way in time. So what was it?

"Ah~ That was close." A familiar voice purred behind the young boy.

Impulsively Killua rotated and saw the slim figure of the man who had betrayed him. He stood proudly at the end of the hall with a waving hand and a shit-eating grin to follow. Hisoka, that bastard… but did he really save him from getting hit by Illumi's needles? He didn't even feel him-

'Wait… he couldn't have!'

A spiral of Nen surfaced and covered Killua's eyes, revealing a pink aura shaped like thread leading from his back to Hisoka's right index finger. Bungee Gum. When did that clown attach it to his back?

Hisoka tilted his head in question to the location, but did not voice his opinion.

Instead he walked up behind Killua and gently pushed him forward with his hand on his back to get him moving. The trace jolted the young Zoldyck, and he griped under his breath while approaching the entrance doors that had been sloppily boarded up by the previous owners

Back at the time they arrived! Killua grit his teeth at the memory, however he couldn't scold Hisoka for his trickery. In fact he should have been thanking the magician for saving him the pain that could have been inflicted.

Hisoka kept his distance, and shifted his gaze to the long haired male exiting the room which the needles came out of prior to Killua's rescue. There was no hiding his presence now that he'd been discovered, but this knowledge didn't seem to deter the sadist. In fact his grin inhumanely spread when a low chuckle erupted from his sly lips. He'd done his part as promised, and until the end he would no longer interfere. After all he didn't want to get on Illumi's bad side – or rather stay on it too long. It would be bothersome with future plans between the two of them. Killua understood this by the fashion Hisoka started to back away and serenely put his weight against the wall behind him.

"Oh, continue." The red-head mused with desire.

Illumi didn't appear happy by his wish and his dark orbs narrowed into an unrecognizable glare. Although to others his expression seemed unchanged. Gold met black, and their eyes locked into a solid death match.

Killua didn't take any moment for granted and regained his footing as a twist of electricity spiralled around his arms to show his offensive measures coming to light. He bounded forth to Illumi and threw his palms closely together as currents surrounded the outstretched limbs, 'Lightning Palm'. He was inches away from hitting Illumi in the abdomen before he jumped back to avoid it. He'd missed him but not by much, resulting in various streaks lashing out and hitting Illumi where Killua had directed his attack. It didn't appear to hurt him badly, but it kept him from moving too far.

A disappointed rumble echoed from the young boy, and he ran towards his enemy in another attempt to disable his movement. However his chances had run out, and the assassin mirrored Killua's attack with excessive speed and kicked him square in the stomach. The power administered in his strike held force brutal enough that it swept him across the ground, tumbling into a wall.

Killua knew that at least one or two of his ribs had been crushed from the impact. He rolled over and managed to get up on his hands and knees, coughing up spots of blood that managed to make its way through his system. The maroon liquid glistened in front of him, and his head swam with incoherency from its collision with the wall. Quickly the boy shook his head and looked up to see his brother standing in front of him, but wasn't given any time to act when Illumi grabbed him by his collar.

He picked the silver haired child up and threw him coldly against the wall, further abolishing it with his raw power, but he didn't finish there. He held him in place, black eyes looming over his figure.

"Kil. Where did that strength go?"

"L-Let go of me!" Killua yelled at the other. His voice caught in his throat when Illumi's grip moved up to his esophagus, and slowly began to strangulate him. No words could escape the boy, except a strangled grunt of reinforced obstinacy. Pale hands reached up to grab hold of his brother's and move them away by force, but to no avail did he have the strength to surpass Illumi's. The grip tightened and he gasped with little air he had left. He knew Illumi wouldn't kill him, but that didn't mean he wouldn't make him suffer to hell and back.

Illumi pressed forward with his questions, his face close to Killua's, "What made you so angry before?"

"Shut up!" He shouted in refusal, pouring out all his strength. He had always respected his brother, but by no means would he when he threatened his friend.

"Was it Gon?"

"I said shut up!"

"If I kill him, what will you do?"

Silence followed throughout the hall, all except Killua's quiet struggle to be released.

The inquiry clogged Killua's already questioning thoughts, and he opened his eyes to stare into Illumi's reflective orbs. They knew deep down the young hunter would be lost without his friend, though neither admitted it in the form of words. A brief look of sorrow covered the younger Zoldyck's face, and he dropped his head down in defeat. If Gon died, he would have nowhere to go further in his journey; nowhere but home on Kukuroo Mountain.

His body crumbled to the ground when Illumi let go and stepped away from him. He gasped for air, barely able to hold himself up with the support of his shaking arms. When he'd lost it in his fury, Killua used up so much of his power it left him exhausted with hardly enough energy to perform 'Thunderbolt'. He had recklessly used up his abilities and it left him on the ground with no defence against Illumi. Is this how it would end? He'd lose and Gon would die. Because he was weak… he couldn't kill his brother and save him.

He wanted to run… to flee in the face of a stronger being than himself. There's no possible way for him to defeat his brother, so what more could he do now? He can't save Gon at this rate! Maybe he shouldn't have come… there's no use… but…but what more could he do?

"Dammit…" Killua's voice wavered and he stared distastefully at the ground. "Dammit…dammit…!"

Is this all he could really do in the end?

Is that all?

Is he…really that weak?

'The Killua I know wouldn't run from me and make excuses.'

Gon's words slowly began to echo in his head. They were so sincere…

'The Killua I know wouldn't lie to me!'

His emotions at the time, his words, and the look in his eyes; everything about Gon blinded him in a warm, honest light.

'He'd trust me with his life when we fight against really strong enemies! He is my best friend in the world and I would fight for him no matter what!'

That's what he said back then…Killua is… his own person.

He is headstrong, quick thinking and most of all an honest, caring friend to Gon Freecss.

Even if he wasn't there, Killua felt as if his friend's hand was lying on his shoulder, urging him to continue fighting. He believed in him when he had no belief in himself. When all of his light had faded away, Gon shared his own. He had always been there for him… his best friend in the whole world. The one person… he would absolutely not let down, no matter who or what he was up against.

If Gon was there, he would fight for him when he was down. He would wait until he could get back up, using his own body as a shield until he could stand on his own two feet. That's the kind of fool Gon was, but he was the one who had dragged Killua out of the darkness many times – the boy who had saved him.

Killua smiled genuinely at his thoughts.

Like Gon had saved him so many times… it was time he saved him.

Turns out I might end up making this a little longer!

Jeez I'm bad at organizing chapters aren't I? I should make up for it by ending this at 14 chapters instead of 12!

Reviews are welcome! They really help motivate me to finish this! :)