Outside of Thirteen's mind~
Thirteen's breathing was getting quicker and quicker as a crazed grin rolled in on his face, Zoro grabbed his swords, Sanji stared at him with tensed legs, and Luffy looked at him while Nami and Usopp didn't realize anything was wrong.
Usopp pulled Thirteen's eyelids apart, holding a flashlight to see if they were damaged before falling back as both of Thirteen's pupils were blood red. Nami said quickly "What's wrong?!"
Sanji was silent, Zoro didn't know, and Luffy said "The same thing happened with Mihawk before." Sanji added "He just went crazy. Poof, just like that." Usopp trembled and scooted back, mumbling "How dangerous is this guy?!"
Zoro chuckled and said "Shouldn't be too bad. Maybe I can test out my new swords." Nami shouted "Usopp! Get back here! He still needs help!" Usopp stuttered "W-What if he eats me!?" Nami smacked him and said "I'll throw you in the sea before he can do it, if you don't help!"
Usopp gulped and crawled over, continuing to bandage Thirteen as Luffy watched carefully. Zoro and Sanji were ready for anything and Nami held Thirteen's head on her lap, mumbling "Please…"
Inside~
Thirteen was beating on nothing as the other him watched from the side, cheered him on, saying "You got him! Get angrier! Eheheheheheh~ Just a bit more!" as he licked his lips in anticipation feeling that he was about to take over.
Suddenly, Thirteen stopped and turned to the other him, who snapped his fingers and said "Awww… So close~" before laughing as he dodged Thirteen's charges. The other him, grew a maniacal smile as he said "Come on, come catch me, hhehehehe~"
Thirteen pounced at him as the other him commented "We're the same~ Hehehe~" before blinking and kicking Thirteen in the back of the head, sending him flying as the other him jumped and danced, humming to himself.
The scene changed to the island where the boy was sold and they were on a beach, the other him skipped around kicking Thirteen around and dodging his attacks, singing crazily.
Thirteen rolled on the ground and stopped by the water, letting it crash on him as the water turned dark. The other him skipped over and jumped onto Thirteen, stomping and pouting "Awww.. You're done playing?"
Thirteen was unresponsive and the other him clicked his tongue before kicking him again, saying angrily "Keep playing with me!" Thirteen's body skipped on the water and stopped on top of it as the other him walked over, treading water.
He stopped and crouched down, grabbing Thirteen's head, saying "You're so boring. Why can't you just let me take over, forever? Imagine all the fun we could have! You can stay here and watch!"
He sneered and added "You don't even know what fun is, do you?" before clicking his tongue and continuing "That's right, you emotionless freak. You can't have fun, only I can! So why are you in control!?" before smashing Thirteen's face into the water and holding it under, rambling on "You can't even feel! What's the point of you!?"
He pulled Thirteen's head out and watched him cough as he continued "I have all the emotions! You have nothing! Let me out!" Thirteen coughed and said weakly "No. Get out." the other him's face contorted in anger and he drowned Thirteen again, shouting "WE'RE THE SAME!"
He brought Thirteen's head up again and Thirteen coughed, saying "We're not. You're a monster." The other him shook with rage and started laughing as he shouted "I'm a monster! HEHEHEHEHEAHAHAHAHEHHEAHH! Take a good look at yourself!"
Thirteen looked at the water and his pupils were red just the same as his other self. He closed his eyes and said "It's fake. You're not me." the other him clenched his fist and stood up before kicking Thirteen, saying "Idiot."
Thirteen flew through the sky and smashed through the sunset, landing back in the black space before intense light appeared all around him.
Outside~
Thirteen opened his eyes and stared at the sky as he heard Nami say "He's alive!" He looked around and sat up, noticing everyone was looking at him. He turned to Usopp, who was scared stiff and saw his reflection in his goggles.
Noticing his blue pupils he turned back to the crew and nodded at them. They let out a breath of relief, secretly, before Luffy grinned and shouted "Look! A giant waterfall!"
Nami turned around and shouted "We're gonna crash!" as the ship veered to the walls of the waterfall. The crew got into action and started doing everything they could to not crash as the ship slowly veered back to the waterfall.
Luffy jumped off and blew up like a balloon, pushing Merry back to the middle of the waterfall before being pulled back to the ship and laughing as the waterfall took the Merry into the sky.