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"Oi, Luffy."
Zoro climbed up and joined his captain on his usual spot at the head of Thousand Sunny. They were sailing trough the new world, currently having decent weather conditions. Luffy looked up, staring at him.
"Huh?"
"You've trained Conquerors Haki, right? Use it on me.", Zoro demanded, his arms crossed and face serious. Luffy looked at him curiously. He noticed that challenging glimmer in Zoros eyes he was so familiar with.
"Shishishi!" The strawhat snickered and broke into a wide grin. Zoro looked very sincere about this, and it filled Luffy's chest with an intense feeling of pride for his friend. Zoro wasn't doubting him as a captain. It was a test. A test both for Zoro himself, if he was good enough for the future pirate king, and for Luffy, if he had what it took for Zoro to still trust his life and dreams in him. And Luffy was more than happy to confirm that both of them were strong enough for each other. He himself didn't need that confirmation, but he knew Zoro liked to challenge himself and others.
"Alright, here i go!"
He stood up and placed himself in front of Zoro, opposing him. His stance was secure and confident, but so was Zoro's. The swordsman mentally prepared himself for anything. Luffys face got all serious, he took a breath to focus and then opened his eyes to intensely stare at Zoro.
The first wave of Haki rushed over Zoro like the tides of the ocean. It felt like gravity was increasing, like his chest was tightening, like his mind was becoming overpowered by the raw energy Luffy emitted. He stood his ground, sure, didn't even flinch. But he definitely felt the insane pressure and willpower that was forced onto him. His body felt heavy, like it was pushed into the ground by invisible forces. He could imagine how weaker minds would just give in to this might, how it was easier no to resist. How it would crush anyone not mentally prepared for the Grand Line.
This was the force that had defeated thousands of men on fishman island in mere seconds. But it was easily handable by Zoro, and he knew it wasn't all Luffy had to offer, either.
Luffy seemed to understand Zoros thoughts, as usual. The swordsman wanted more, more to measure himself with, more of a challenge, more proof that Luffy was the man he rightfully put his faith in. He increased his Haki's power. The ocean water below them started to be pushed away from the Sunny.
Zoro felt the Haki double it's might. He heard a faint thud somewhere on the ship, but it was distorted, dull and far away, through a fog of Luffy's aura. The force made Zoros knees wobbly, his body strain. It was enough to stop the powerful beasts and monsters dead in their tracks, and to command and control them. The swordsman was amazed by the power of his captain once more. Luffy usually seemed so cheerful and careless, so the crushing, dominating waves that zoro was now experiencing were kinda out of character. At the same time, they were not. Zoro knew Luffy was an incredible human being and a strong leader, so obviously he would be able to stand his ground to other people, be it by haki or not.
Gravity still seemed to increase and the world was shrinking down unil it was just him and Luffy. Zoro could not concentrate on anything else, it was like being unable to look away from something. Not that he could afford losing his focus anyways. The Haki was pulling on the edges of his very consciousness, making it hard to think. Zoro gritted his teeth. Breathing was getting harder, too. Zoros hands were tightly clutched around his arms, constantly increasing his grip in his struggle against Luffys Haki. His vision was becoming slightly blurred and everything seemed to slow down.
Luffy, too, was straining. Using Haki for a prolonged time was still exhausting. However, he knew Zoro would only be satisfied if he either was defeated, or managed to prove himself. And so, he increased the power of his Haki yet again, giving it all he got. (Or at least all he could muster in this non-life-threatening situation. It was very different from a battle, after all.) His willpower was all-consuming, lying over the area like a haze. The Sunny was pushed a few foot into the ocean's surface. The world became quiet.
Zoro dropped to his knees under the pressure. He held himself up with both arms, trying to strengthen his mind so he wouldn't pass out. It was a weird feeling, having someone elses mind forced onto him. His consciousness was being invaded. At the same time, Luffys presence was so incredibly familiar with him, yet multiplied into infinity, almost unable to bear. It truly was like the ocean. It perfectly mirrored Luffys compassion and affection for his nakama, turned into his insane drive in battle against his opponents. Zoro experienced all of this right now, unable to move.
His heart was aching, not only from emotions, but from the ever increasing pressure of Haki in his chest. His skin hurt. His vision was slipping, his thoughts unravelling. He could barely hold on to himself anymore. He felt like he was drowning, drowning in the ocean that was Luffy and his ever-growing willpower. Yet, he hadn't passed out. Or had he? The world seemed to spiral inwards.
Then, suddenly, the pressure lifted and Zoro snapped out of it. It felt like a giant weight suddenly disappeared, or like he was pulled back up on an invisible string.
"Zoro? Zoro?"
He was breathing heavily, lying on the floor. Slightly desoriented, he quickly gathered himself and collected his thoughts. He looked up and saw Luffy, who was also out of breath. He looked exhausted, but as he noticed Zoro being aware of him again, a smile spread on the younger man's face. He looked proud. "Zoro!"
Zoro blinked at him for a few seconds, then managed to get up and brush off his clothes. He felt slightly dizzy, but that disappeared after a few moments. He looked back at Luffy. Yep, that was definitely the one person he would give up his life for. Zoro grinned.