Burning, tearing, stretching, blood. Pain. Excruciating, horrible, terrible, unbearable. Pain. Painpainpainpainpain.
Zoro thought he understood sacrifice. He spent hours every day pushing his body past what should be his physical limits. He had left behind his home, teacher, and everything he knew to pursue a dream. He had not allowed himself to be stopped by hunger, thirst, or physical injury. The reputation of a demon followed him, all because he had pushed everything aside to pursue a goal and keep a promise.
The Straw Hats had questioned that assumption. Before meeting Luffy, Zoro had never put any thought into the word 'sacrifice'. It's just something one did if they wanted to be the best. If Zoro knew anything at all it was that strength requires work, work requires effort, and effort requires determination.
But Zoro had never in his entire life given something up for someone else. He had completely meant the ultimatum to Luffy before joining his crew. Letting anything get in between his promise to Kuina was unforgivable. After all, he had already given up so much on his journey.
That's why it was interesting to him to see what the others had given up. He had never put his dreams on hold for someone else like Nami or Franky, or put off training to see to other people's needs like Sanji did on a daily basis. He never tried to take on or ease other another's pain like Usopp and Chopper, nor surrender without a fight to save his companions like Robin had. Hell, even the skeleton had given up the peace that came with death to reunite with a lost friend (if whales could be considered friends, which by Grand Line standards wasn't all that far-fetched).
And while Luffy might not have been too keen on keeping everyone safe (because, you know, adventure) he would protect their dreams with his life.
Sure he was completely loyal to the crew and would fight to his last breath to keep them safe, but even when he was protecting the others it served to make him stronger and further his dreams. What was the worst that he had suffered as a part of the Straw Hats, an annoying cook? Interrupted naps? A reindeer that seemed to have a love affair with bandages? Oh the horror.
But when the Warlord had stepped foot on Thriller Bark, threatening his captain's life, things changed. Had it just been Zoro present, a fight to the death (probably his) would have ensued. As it was, his crew (family) were scattered about in varying states of unconsciousness. There was something distinctly unfair about having to face two Warlords of the Sea in the same day, a robotic and virtually indestructible one at that, but when was the pirate's life fair?
So he had made a deal. Luffy's pain for the lives of his comrades. It seemed like a simple enough, if somewhat confusing, out to a desperate situation. He was Zoro, the future greatest swordsman of the world. He got almost stabbed to death on a semi-regular basis. What was a little pain against that?
The first little chip in his resolve occurred when he saw what Luffy's pain actually looked like. How the Hell did all of that fit into such a little body? Still, Zoro refused to back down. This was something that needed to be done, and he needed to be the one to do it. Sanji's attempt to give himself up with him had been admirable, but just didn't sit well with Zoro.
Maybe it went back to that sacrifice thing, or maybe he was just looking too much into it.
And then that bastard of a Warlord had casually flicked a small (tiny, really) portion of the burden he would carry. The effect was immediate. Luffy was a rubber man, Zoro most certainly was not. Muscles, organs, joints, and bones were not made to bend that way without the power of a Devil Fruit.
Zoro made a final request, to move somewhere else. It would be pretty bad if any of the others woke up and saw what he was doing. He knew no one else in the crew, save Luffy of course, would be able to handle what he was about to do.
In the secluded location on the giant ghost ship Zoro took a final deep breath, and focused on his inner strength, the place that held his determination and willingness to go forward. Then he shoved his hands into the paw shaped bubble.
Pain. Gnawing, breaking, deep, visceral, pain. Stabbing, shearing, indescribable, pain. Pain, pain, pain, painpainpainapianpainpainPAIN!
He took it all without complaint. This was his burden, his sacrifice to make, because for the first time in…a very long time he had a family. Everyone had a role, and this was his. He was going to be the greatest swordsman in the world, a fitting title for a crewmate of the Pirate King.
Even as he was beginning to be overwhelmed and on the edge of consciousness, Zoro knew that this alone wouldn't kill him. Luffy had borne it easily, taking it as a part of being captain. Zoro had sworn to follow Luffy and protect his crew, and that wouldn't be possible if he was dead.
Because now he understood true sacrifice, the willingness to give up everything for another, and that understanding made him stronger.
And Zoro, the man who would surpass Mihawk, would sacrifice everything for his family.