Hi! Here's my first LawLu angst, as I wrote it around 4am there might be some mistakes even though my beta corrected it, I hope you'll like it! The prompt I took will be given at the end of the OS.
Enjoy~

Don't die on me

Luffy was exhausted. He could barely hold a normal breath, his body was shaking. He felt his legs dropping, and his strength leaving him little by little, step by step.

Defeated. They'd defeated him. They had actually done it. Honestly, he never doubted it for he was meant to be the Pirate King, meaning he could not afford himself to lose – but man, what a fight.

The Straw Hat Captain sketched a smile, finally relaxing. He was about to let himself fall on the floor, and give up on his fight against unconsciousness, when he noticed he had not seen the Heart Pirate around for a moment. So he turned to his right, to his left, behind him, looking for him.

He was nowhere to be seen.

Luffy's heart began pounding in his chest, and he felt he was about to faint of tiredness. He had to rest. He had to take a nap, to sleep the time he needed to gain his strength back – two or three days at least, more or less – and some food – including meat of course – and everything would be just fine.

But he couldn't do that as long as he wasn't sure Law was okay. After all, he was his ally – his nakama. I couldn't give in now, that'd be like a betrayal. The young man just had to be sure – he knew the Captain of the Heart Pirate would be fine, as he was one of the infamous pirates from the new generation, he could take care of himself – but... but still.

Luffy felt as if he had to make sure of it.

He walked. Slowly, but he did. Sometimes, his sight blurred all of a sudden, and he had to shake his head to get back on Earth. Get back to his current goal. With all of what was left of his strength, he weakly called him.

"Torao. Torao", he whispered repeatedly.

He couldn't take it anymore. The moment he was about to let himself go, he saw him. And froze.

Trafalgar D. Water Law was nothing more but a shadow, a dark shadow lying on the floor a few meters away. A motionless dark shadow.

Luffy took a deep breath as if he was looking for air to snap back to reality, as if he was hoping for this vision to be an illusion of his body's state. He had used too many Haki, and if not Rayleigh and his crew, Law himself had warned him about the consequences.

Somehow, he found himself on Law's side, a concerned look on his face. Maybe he had run, maybe he had used his elastic powers to get here, he didn't know nor remember, and he didn't give a damn about it.

"Torao!" he screamed in a more certain tone. "Torao, answer me, are you okay?"

The young man couldn't help but think about the second time they'd fought together, after Sabaody, in Dressrosa – against Law's worst enemy, Doflamingo. That one time he had just finished his 'fight' with Bellamy and joined his ally just to find him... dead.

He remembered the warlord bastard about to crush his head with his foot, full power on, and him stopping this mortal threat. He remembered Law, being carried away by the strength of the attack, and he remembered how he felt the moment he had found the pirate covered in blood, breathless. One arm missing.

His heart had stopped.

"Can't you see?" Mingo had said. "He's dead. That's pretty damn obvious."

"Liar!"

This time, he hadn't believed the Shikibukai. Because Law was his friend.

"By the way, he really seemed to trust you. He said... you could make miracles."

Because, in spite of everything they could have said, Law was more than that. Dead. Dead? Impossible. No way. His nakama couldn't be dead. He was not supposed to die. Because Luffy had come here to fight with and for him. And Luffy was no man to fail his promise. Law couldn't die on him.

"You're lying!"

He remembered anger flowing through his body, he remembered rage, hatred and pain. The Captain remembered he had wished to never fell like that again. This... feeling, way too powerful for him to fully understand it, or even trying to control it. He just couldn't. He couldn't live this moment again. He couldn't allow him to...

"Torao, hang on! I'm gonna- Don't leave- stay with me!"

He moved, and Luffy felt like reviving.

"Luffy-ya..." he muttered.

"Torao, what happened?!"

The former warlord coughed, and Luffy put one hand on his in order make him know he was not alone – to remind him that he was here, and that he needed him.

"Just... couldn't hold it..."

"It's okay," he assured, and he smiled.

And for the first time, Law realized he had never thought he'd see a fake smile on Luffy's face. And yet, there it was, this smile, which cried more than it smiled... Even when he was trying to make you feel better, his face was betraying him. He was such a bad liar.

"I'm sorry I'm letting you down," he said.

"You're not!"

Truth was, they both knew they couldn't know if Law'd make it or not. This fight, he had just used his powers too much. It was taking away his life, sucking it away like a leech.

The Straw Hat couldn't take more of this.

He broke down.

"Y-you can't do that to me," he said, sobbing. "I-I'm gonna take care of you. Chopper's gonna take care of you! He's a great doctor, you know. He'll heal you...!"

"I know he is. I know he will."

Luffy leaned on to finally fall next to him, and cried on his shoulder, releasing all the tension, the anxiety and the sufferings he'd been holding back for so long. They had worked so hard to get to this. They had fought so wildly.

"Please, don't die on me, Law."

The other Captain couldn't help but open his eyes, surprised. He then smirked, stroking his hair.

"I will not, Luffy-ya."

The prompt was: "Person A is hurt by a big bad when fighting. Person B carries on fighting, not knowing Person A is injured. When the battle is over, Person B turns to celebrate with Person A, only to find her/him bleeding out on the floor. Person B holds a very hurt Person A." I didn't want to give it not to spoile the whole OS.
Let me know your thoughts about this!