Author's Note:

To the Guest: Of course! Who wouldn't? *hides under desk* Thanks a lot for reviewing! :D

Also, this chapter might or might not end with (one last) cliffhanger, and thus you might or might not want to wait for the next chapter before reading that one.

On a more general note, I have three chapters left after this one, and I'm hoping to have this fic completed by the end of the year.

At your Core

Karai couldn't believe her eyes. Part of the ceiling had collapsed in front of them, isolating their part of the cavern from the rest. Leonardo and Raphael were both on the other side, with the Shredder.

Seriously, Leo? she thought with indignation.

But she couldn't dwell on that. She had more pressing matters to attend to, like the pain she was beginning to feel in her injured arm. Focusing was becoming harder.

"Let me help you," Angel said. "I've experience with first-aid." She picked a small pot from the purse at her belt and put it on a nearby rock, along with bandages.

Karai would have welcomed any help, experienced or not, so she was all too happy to let Angel handle this.

"I can't hear them," Spike suddenly said. "It's like we're completely alone."

Karai listened as Angel removed the ice shard from her arm and applied some liquid from the pot - from the way it hurt, it could only be disinfectant. She heard the lapping of water nearby, droplets of melted ice hitting the rocks, their heavy breathes, but there was no sound of Raphael or Leonardo or the Shredder, or anything resembling a fight.

The rock barrier must be too wide. At least it probably meant that the Shredder couldn't reach them anymore - which was no doubt what Leonardo had wanted.

"Then we're on our own, and we should do our part," she said between gritted teeth. "Leo suggested looking for the other firebenders. I'll stay here to melt my father's ice block, but I don't need everybody's help."

"I'll stay with you," Angel immediately said as she finished bandaging Karai's arm. "I want to keep an eye on your injury." She gave Karai a warning look. "And make sure that you don't overwork yourself."

Karai didn't bother answering that.

"I'll try to find the others," Slash said. "I'll follow the shore towards the end of the cavern, see how far it goes. I'll yell if I find anything."

Spike gave a heavy sigh. "And I'll investigate the other part of the shore."

It was obvious to Karai that he would have liked to stay with them, but he must be as aware as everybody else that they had a limited amount of time.

"Be careful," Angel told them both. "I don't have medical supplies for everyone."

"It's already great that you do have some," Karai said as the two teenage boys departed in opposite directions. "What made you think of it?"

Angel shrugged. "I always carry them. After my dad's accident, I… I wanted to make sure that I could help people when they got hurt."

"I see," Karai merely said. She pressed Angel's shoulder with her free hand.

She tried moving her bandaged arm. It hurt, and she couldn't extend it completely, but she could still firebend.

She started melting the ice block again.

In what state would her father be? She had no idea what kind of damage the ice would do to the body. Externally it preserved them, but internally?

Her father was a powerful firebender. Hopefully he had used his bending to keep himself alive.

Karai held onto that belief as she kept melting the ice block, trying not to think too hard about what was happening on the other side of the rock barrier.

Leonardo felt cold. So cold. From his toes to the top of his head, from his waterbender's hands to his raw-from-yelling throat.

And it was all because Raphael wasn't sharing his warmth with him anymore - because Raphael couldn't share his warmth with him anymore.

Raphael who was watching him, his eyes wide and utter horror painted on his face, as he was creating a fireball bigger than Leonardo had ever seen.

At first, Leonardo hadn't understood what was happening. What was the Shredder doing to his brother?

And then he had remembered how April had shown him that saliva could be bent, that everything akin to water could be bent, and he had understood.

Blood. The Shredder was bending blood.

In the corner of his mind that wasn't freaking out, Leonardo wondered whether the Shredder was the only one able to do that, or whether every waterbender could do the same.

The thought was appalling.

On his ice platform, Raphael raised his arms to throw his fireball.

"Raph! Keep fighting him!" Leonardo shouted as he forced his tired arms to waterbend his own ice platform out of the way. He had expected resistance from the water - he had had to fight the Shredder for control over even a little part of the water below - but there was none. Maybe water… Maybe bloodbending required the Shredder's whole focus.

Still, Raphael's fireball missed him by mere inches. Leonardo had barely the time to stabilize himself on the ice again that Raphael was already starting another fireball. Leonardo knew his twin was doing his best to resist, but what if he didn't manage to break out of the Shredder's control in time? It wasn't like Leonardo could keep up that game for hours.

Leonardo felt despair crawl inside him. What had he been thinking? That he stood a chance against the Shredder, even if that chance was only to survive long enough so that the rescue party could arrive?

He had been a fool, and this total disaster was his reward.

This was a living nightmare, one Raphael never had, not even in his darkness nights. He was using his firebending, the ability he was most proud of, to hurt his brother.

Raphael fought with all his willpower, but his body wasn't his own anymore.

Leo, he called in his head. Leo Leo Leo. Help me. Please. Leo!

His twin was desperately trying to keep out of the way, and all Raphael could do was watch him.

As if he could feel Raphael's despair, Leonardo raised his head and locked eyes with his brother.

"Hold on, Raph! We're going to make it," he said.

Raphael knew when his brother was trying to lie, but he appreciated the intent.

The ice around her father's body was almost entirely gone now. Karai bit her lip as she and Angel lay him down. The body wasn't as cold as she had expected it, which had to mean that her father was still alive.

She knelt next to him, trying to warm him up as slowly as she could while Angel was holding his head with both hands.

Come on, Father, Karai thought. Wake up. Don't let me lose you.

When Saki blinked and straightened up with a groan, she couldn't stop the tears from escaping her eyes.

"Karai?" Saki said, slowly. "Where… where am I? What happened?" He frowned as he tried to remember. "We were trapped, and…" He took in their surroundings. "Where are we?"

Then he seemed to notice the sparkles flying around his daughter's hands.

"What are you doing?"

Karai wiped her tears and met his gaze fiercely.

"I'm saving you."

Saki looked appalled, and his expression became even more somber when he noticed the bandage on her arm.

"You're hurt."

"It's nothing," Karai muttered, embarrassed.

Saki bit his lip, as if he wanted to say much more but had realized it wasn't the right time.

"How did you come here?" he asked instead, looking alternatively at Karai and Angel.

"We came through the mountain," Karai said. "But our exit is underwater now, so…" She shrugged. "We'll have to find another one, I guess."

She wanted to hug her father, but it didn't seem like he would have allowed it. In fact, he looked absolutely furious, and that wasn't fair.

"You found a passage through the mountains?" Saki said slowly. "And you took it? Just the two of you?"

Karai exchanged a glance with Angel. "Well, not exactly. Spike and Slash are here too, looking for your warriors."

She didn't miss her father's grimace at the mention of the firebenders that had accompanied him.

"And Leonardo and Raphael came along too," she added.

Something in her voice made her father frown even more.

"Where are your cousins?" Saki asked, slowly, as if he feared to hear the answer.

Karai turned to watch the wall of rocks.

"On the other side," she whispered. "With… with the Shredder."

She expected Saki to ask her about the full story, but her father was speechless.

The distress Leonardo was reading on Raphael's face was unbearable. Leonardo kept eye contact with his brother, telling him everything that went through his head while he tried to figure out a way out of this situation, refusing to look away even as he was dodging the second fireball.

And he immediately noticed that something was off about that throw. It wasn't to the level of Raphael's usual firebending performance; the moves were wrong, a bit like Leonardo used to do them.

The realization hit him hard. The Shredder didn't know firebending well enough to give Raphael's strikes their full potential. It was good news, even though Leonardo wasn't sure it was good enough news.

He briefly wondered whether he could plunge in the ice-cold water, swim to his brother and bring him into the water too. Maybe the Shredder needed eye contact with his victim so he could bloodbend?

But then, both he and Raphael would be at the mercy of the Shredder's superior waterbending. And even if Leonardo could somehow prevent them from being destroyed, what would prevent the enemy from bloodbending again as soon as they would leave the water? It wasn't like he could stay underwater forever.

Once more, Leonardo regretted that he didn't have the time to watch his ancestor Karai's memories to the end. What had she done to weaken the Shredder? From what he had seen, she had taken something from him - but what?

He felt a sudden surge of energy through his tired body. It was like an ancient and soothing presence was watching over him, giving him more power.

The moon. Leonardo couldn't have explained it, but he knew it was high in the sky, and it was full. Its power was sustaining his failing strength.

But of course it would be the same for the Shredder.

Leonardo glanced at his enemy. The man was smiling brightly, which was a terrifying sight in itself, but it wasn't what caught Leonardo's attention.

Something was pulsing a dark blue on the Shredder's chest. Leonardo narrowed his eyes, trying to see what it was, but it wasn't like he had all the time in the world.

He dodged another attack from Raphael by pulling a wave in front of him, like he had seen the Shredder do.

Something blue flew to Leonardo's hand, and Leonardo realized it was the crystal that had chosen to travel with him. It had been strangely silent lately, and he had completely forgotten about it.

It was pulsing at exactly the same rhythm as the thing on the Shredder's chest. Had the Shredder his own crystal? Was he drawing power from it, in a way Leonardo didn't understand?

Maybe his ancestor Karai had managed to take it from the Shredder at some point, and maybe the Shredder had managed to take it back - but not before he had been too weakened to keep fighting.

Leonardo would have tried to do the same, but he was never going to be able to move close enough for that, either with his bending or in person.

The crystal in his hand was still pulsing, its color a bright blue, and its edge pointed towards the Shredder.

On an impulse, Leonardo threw it towards the Shredder. He immediately regretted it - the Shredder was too far away, and anyways he wasn't going to be hurt by such a tiny crystal - but the crystal kept flying, even though it should have fallen into the water.

Then it reached the dark blue light on the Shredder's chest.

It is said that in the ancient times, a water spirit fell in love with a waterbender woman. This love was mutual, but her tribe didn't look on it with a favorable eye. They decided to get rid of the spirit, and as he was very powerful, they tricked him into thinking the woman he loved had married another man in his absence. His heart froze and broke in two crystal pieces. One fell into the ocean; the humans threw the other in the deepest hole they could find.

When the woman realized what they had done, she forsook them and left, sailing for days and days until she reached a peaceful island. As she rested on its beach, she found a beautiful crystal that pulsated like the heart of her lost love, and she knew she was here to stay.

She built a home and then a school, because she was well versed in the waterbending arts and she liked to teach, and the crystal never left her. When she died, she was buried with it against her heart. Time passed; decades, then centuries, and her story became legend, and the legend became mere whispers in the wind, until the wind spirits who told it hid from this world like the fire, water and earth spirits.

But the crystal remained, and one day it was found, by a waterbender whose heart was so dark it couldn't recognize it for what it was. He understood its power, though, and he used it for his own purposes.

There were no legends told about the second half, and it wasn't found until much, much later, but found it was, and it longs to be whole once more.

As soon as the crystal reached the Shredder, the whole cavern was engulfed in a bright light. Leonardo closed his eyes, feeling its warmth on his skin and within his soul. Then it vanished, and Leonardo hurriedly opened his eyes.

In front of him, Raphael was collapsing on his ice platform. Leonardo barely had the time to jump towards him and catch him before he hit the ice.

"Leo," Raphael whispered. "Are you… okay?"

"Yes," Leonardo said, hugging his brother.

"I'm… sorry," Raphael slurred. "He was controlling me, he…"

"I know." Leonardo tightened his hold on his brother. "It's not your fault."

Then the Shredder roared in outrage, and Leonardo knew he had no time to comfort his brother or himself.

How could this have happened? How could this stupid child have destroyed the Shredder's most prized possession, the power source that elevated him above mere mortals? Even his daughter, Karai, had only managed to steal it for one brief moment.

They were going to pay for it. The Shredder had played enough; it was time to kill the enemy.

It wasn't over.

It wasn't over, and Leonardo was exhausted.

Raphael wasn't any better, but he still tried to straighten up and take a fighting stance.

The Shredder was rushing towards them, murder written all over his face, and Leonardo knew they were done for.

After everything they had accomplished, they were still going to lose.

To die.

The Shredder threw a shower of ice shards at them, and Leonardo jumped into the water with Raphael, just because he wanted to try something - anything. He felt the water around him begin to freeze, and he fought it - and Raphael fought with him - but they could only slow it down, and now spikes were forming on the ice, and they were progressing towards Leonardo and Raphael's exposed flesh.

Right before Leonardo's last bit of strength abandoned him, he thought he heard the blurred voice of his father calling his name - a last, cruel auditory hallucination.

Sorry, Dad, Leonardo still thought. I really did my best.