Inside the prison
There was a pair of keys floating in the air being swung around as if they were on someone's finger. They floated throughout the hallway before stopping in front of one particular cell. A little 8 year old boy looked up, he was very pale as he said "G-g-g-g-ghost!!!"
"Pfft, Wahahahaahahahah!!" a loud laugh rang out in the prison as Kai revealed himself holding the keys. "I thought you said your dream was to be an invisible man? How can you be scared of your own dreams?" He sighed and shook his head as if he was truly disappointed in Sanji.
The latter was sitting in his cell dumbfounded at the current situation before he finally asked "Kai? What are you doing here?" a large smirk appeared on his face "Breaking you out." he said as if he was answering a stupid question.
Two minutes later the cell was completely open and Kai used his ability to fly through the compound at breakneck speeds. He also used his control over the air to surpress the sound that he did make. He appeared in their mothers room without a sound or anyone seeing them as if they teleported. A small smile cracked on his lips he usually can't go all out.
Sora looked at the two with shock for a second before a large smile appeared on her face. "What else are you hiding Kai?" she asks in a joking manner not expecting an answer.
"I really did learn how to read the ancient language." He replied while looking at her deadpan. Sora's smile fell from her face as she muttered "Why am I even surprised with this kid?" before shaking her head and turning to Sanji. A smile returned to her face as she looked at him.
"Sanji, I love you so much. You three are the only lights of my life keeping me out of the dark. I wish I could have some more of your delicious cooking again. I can't believe how fast you grew up and how much your cooking improved. You're going to be the best chef in all four blues!" Kai interrupted. "And the grand line!"
Sora smiled again before finishing. "Of course how could I forget the grand line. I'm proud of you Sanji. You are the most kindhearted boy I have ever met and that's my favorite part about you. You're very different from your other three brothers, but that's what I love about and what makes you special. I don't care if you're as strong as them or if you can fight and kill like them. I'm proud of you for who you are, the little kid who fed the rats in the castle and would make me food so that I could get better. You're going to go on a fun adventure now and explore the wide world. You will see lots of new exciting and fun things from now on but never forget that the thing that makes you special is your kind heart and your yummy cooking! I love you so much Sanji. You are my pride and joy and I don't regret a thing" She said the last part while looking at Kai which caused him to have a sad smile on his face.
There was a noise outside as the guard discovered the missing prisoner. "We have to go now Mom. I love you. Make sure you watch over us and Rei. I promise we will make you proud. I couldn't have gotten this far without you." He said with a smile on his face and tears in his eyes.
"I know you will."
Kai used his fruit to find where Judge was, he took Sanji there and turned invisible while standing right beside him. Judge turned around to see Sanji standing in front of him alone and was confused. It was completely silent. They were leaving earlier than in cannon so they weren't climbing the red line or in the middle of a fight.
"I'm leaving!!" Sanji screamed as he steeled his resolve to leave with Kai.
"An ordinary boy like you is not strong enough to survive on his own on this sea, or in any sea. You will die!"
"So what? You can't stop me!"
"On the contrary I appreciate it. I suppose I am only human as well. Too soft and sentimental to dispose of my own son myself, even if it's a failure like you. But if you disappear of your own volition will not stop you, But as your father I ask one thing of you. Never mention that you are a Vinsmoke! You are a black mark on my success and my secret shame! Do you understand me?" Judge's voice boomed in the hallways.
Sanji's tears fell to the floor. His fathers word just now destroyed the last miniscule shred of appreciation and debt he felt towards Judge and Germa for raising him. Just then Kai appeared behind Sanji.
"Oi, asshat! What the fuck you do mean you wouldn't kill your own son! How many fucking times did you choke me out you dead beat, dickless, fuckwad! If Mom didn't stop you I wouldn't have lived to one year old! You're such an idiot that you couldn't even turn me and Sanji into your little mindless robot freaks who suck your dick for food! I bet if Vegapunk was here none of these mistakes would have happened! He was the one who figured out the genetic enhancements anyway! Too bad he kicked your ass out because you were too slow to ever recreate his work!"
Judge froze as he heard his own son's words. He was pissed. Too pissed to even realize Kai shouldn't know about anything he just said. Judge started shaking in anger as he charged at his kid. Kai saw this coming from a mile away with his fruit and turned invisible before flashing behind Judge and swinging his arm in a downwards motion a blade of compressed wind formed into an arc like shape and flew toward Judge's neck. But Judge adjusted at the last second causing the wind blade to cut from the top of his right shoulder down his back all the way to his left hip.
Judge felt a sharp pain in his back and spun around to smash his fist back to where Kai just was. Only to hit nothing. He looked around to see that Kai was already back behind Sanji. Kai cursed under his breath because that was his only chance to kill Judge for years and he knew it. He just didn't have the power to one shot kill someone in the special Germa suits. Although he knew if he continued fighting Judge one on one he probably wouldn't lose, Judge would never let that happen.
"REIJU!! Kill the fucking brats Keiji and Sanji! They are no longer Germa! Nor are they Vinsmokes!!" Reiju, who had no ability to resist his order, walked up to the two with a fake bloodthirsty smile on her face pretending that she couldn't wait to kill them.
"I know your weakness Keiji! You can't hurt your sister!" Judge's lips lifted into a twisted smile as he was genuinely enjoying the moment he could finally end this kid's life.
"You stole Sora from me! It was because of you! Everything went wrong after your birth! You can't even beat your younger brothers! You have never won once! You are a worthless child! You got a lucky shot on me because you have a good devil fruit, but I won't let it happen again! Now that I know you have the power of wind you have no chance left!"
Kai really wished that he could have killed Judge with that hit but he never expected too. He was now fully suppressing his urge to laugh at his own father foolishness. He had been preparing for today for years. He knew it wasn't the time to reveal his cards. His plan was perfect and he was ready. It all relies on this moment. Kai showed a massive frown on his face pretending that he was furious. He looked at Judge and crouched ready to charge.
"THAT'S NOT MY FUCKING NAME YOU BASTARD!!" He roared as he used the air to amplify his own voice. Charging about 40% of his max speed at Judge he pulled back his fist and made a tiny wind blade around his knuckles. However, about 1 meter short of reaching Judge his body was surrounded in pink smoke.
Kai quickly put his plan into motion by flashing at full speed to the other room and bringing back the body doubles. As he left the two corpses on the ground, he grabbed Sanji and clamped his hand over his mouth as he flashed out of the hallway. (He can always use the air and wind to reduce the sound of his movements so I'm not gonna write it after this just assume he does it always because he will. Just like when he flashes it means he uses his powers to increase his speed.)
He took a few deep breaths to calm his nerves as he wanted to make sure Judge bought the performance before he left. He used his devil fruit to feel everything in the room and after about a minute he sensed Reiju give a thumbs up behind her back and Judge gave a smug look. Now all that was left was for his mother Sora to not give away the plan. She had prepared for today and had nearly perfected her acting abilities.
After he could feel the fact that his mother was 'crying' on her knees in the other room and Judge was beaming in joy he flew our of the ship and took his hand off Sanji's mouth. Having already packed enough food maps of the sea and fresh water to survive for weeks on sea he started flying off using the air to make Sanji float next to them as they headed to the red line.