After that Kenshin and the straw hats wen to the New World. The straw hats saw the climate that was even more drastic than the New World and thought, "the 1st half is really a paradise compared to here where the weather is very dangerous to let alone Yonko's and other pirates"
It has been 7 days since they were here on New World and on their way to go to an island when they heard the distress call came which was sent by Kinemon. After that, they decided to go to the island to help.
Like in the anime everything happened but more quickly as Kenshin didn't want them to waste too much of their time due to their carelessness. He also didn't let their body switch as it is too bothersome. He also killed every single one of them as he agreed when he saw the state of the kids especially Mocha who ate the candies knowing they were poisonous.
Kenshin also took all the data of the experiment as to think about in his free time and try to solve it using his past world's knowledge as Kenshin has learned almost everything that his past world has to offer in his 500+ years of lifetime.
The straw hats fought with Doflamingo's minions like in the anime and Kenshin didn't let Caesar alive to revenge the fallen kids. Caesar also told Doflamingo about everything about his situation that Straw Hats have attacked along with Shichibukai Law and Vice Admiral Smoker before he died by Kenshin's hands.
After they have saved the kids from the lab, Law and Luffy make an alliance to defeat Kaido. Baby 5 and Buffalow came and attacked the ship but they got their ass handed by Franky and Nami. And law cut their head and place them in a raft that was traveling the sea using his devil fruit power.
"What are you doing with Straw hats, Kenshin", asked Law and Smoker. To which Kenshin just said what he has said to everyone that he is joining for fun. Smoker didn't say much as he knew the capabilities as he has seen what he can do 2 years ago.
After that, the kids were transported to the Marine Ship. When the time was to leave Kenshin said, "Wait a bit, I have heard Doflamingo will come in a minute. Let's wait here and finish him before anything like this happened ever again".
(I am not writing about Punk Hazard Arc as it is way too boring and lasted this long due to Straw hat's carelessness. And with MC being cautious and overpowered he defeated the enemies easily)
When Smoker, Law, and Luffy heard that, they were alerted. Law was in his serious mode as he will finally get the chance to defeat Doflamingo. After some time Doflamingo came while laughing.
"fufufu… Law and Straw hat are here. Do you think you can defeat me with all these weaklings", said Doflamingo while laughing.
"What about if you add me in this", said Kenshin while coming from behind.
"Blood Devil Kenshin", said Doflamingo while gnashing his teeth as Kenshin has destroyed every of his auction house or others that Kenshin came across.
"fufufu.. I see so you have joined Straw Hats. Okay, I am going now. I don't think there is any reason for us to fight", said Doflamingo while using Sky Walk to fly away from the island.
"Like I will let you escape", said Kenshin while using his own technique similar to the moonwalk of the Marines to rush towards Doflamingo. Kenshin appeared behind Doflamingo and kicked him hard towards the sea.
Doflamingo who was just flying away was sent flying down towards the sea. Doflamingo in the final moment just used a few of his strings to latch with the Navy boat to stop himself from falling. Just as he was about to relax and see Kenshin, he saw that Kenshin was not there.
Kenshin came tot the sides of Doflamingo and kicked him towards the island. He said, "If you could defeat Luffy, then I will let you go". Hearing this everybody was shocked.
"Do you think you can defeat him Luffy. If you cannot then you should just give up on becoming Pirate King", said Kenshin. Hearing this Luffy became serious. Law who was hearing this said, "Let me fight with him 1st. I have to take revenge for Rosinante".
All the straw hats and Marines were on their ship. Kenshin was there just to make sure that Doflamingo doesn't flee as he is a slippery bastard.
After that, the fight began where Law and Doflamingo fought. They were on equal terms but soon Law started to get tired and was defeated while Doflamingo was perfectly fine.
Then it was Luffy's turn. Kenshin has trained the straw hats for about a month and all of them have shown very nice results mainly in Haki and martial arts or sword arts mastery. Luffy's physical strength improved a lot along with his improvement in Haki.
Zoro's sword mastery and Haki are now up to mid Master level. Sanji's haki is about mid Master level but his martial mastery is expert level. And others have their Kembunshoku Haki about proficient to expert level along with Bushoshoku about beginner to proficient Level. Brook also improved his sword mastery to expert level due to years of experience.
(Up to Expert level is easy but after master level, every stage is a lot more difficult. So, that's, why there is less improvement for Zoro and Sanji, compared to others)
After that Luffy's battle started with Doflamingo. Luffy was fighting on Doflamingo. But then doflamingo increased his power and started increasing more powerful techniques which put Luffy into problems.
"Come out now. What's the point to watch the battle from far away", said Kenshin which started everybody present there.
"Arara kids really are scary. You have grown to be a monster", said Aokiji while coming out from far away.
"Says the monster whose fight caused such a natural phenomenon on this island", said Kenshin. Looking at Aokiji he thought, "He really has improved a lot. He is about the same level as me now. That means that dog Akainu also has improved".
Seeing Aokiji everybody was shocked. Luffy and Doflamingto also paused their battle for a moment.
"Ex Admiral Aokiji san", shouted the marine soldiers who were on the ship.
"What are you doing here", asked Kenshin.
"Nothing I just intercepted some distress call so I came to check here. But the main question is why have you joined Straw hats", said Aokiji.
"For fun, if I have to say. Why did you quit marines", asked Kenshin?
"I lost my belief in Navy's justice", said Aokiji looking at the sky.
"So, what are you doing these days", asked Kenshin.
"Nothing much just traveling the world I guess", said Aokiji.
The people present were shocked at how casually Kenshin is talking with Aokiji who has Fleet Admiral level strength. After talking a bit Aokiji and Kenshin looked towards Luffy's and Doflamingo's battle.
Their battle has reached a critical point. Doflamingo has started to use his awakening to transform the land and snow into threads. He used his threads to attack Luffy who was using Gear 4th but more powerful one than the counterpart.
The battle ended like that in the anime but it happened in Punk hazard instead of Dressrosa. After that Kenshin was about to kill Doflamingo when Smoker stopped him saying that it will be beneficial to catch him alive and take as much information as possible. Kenshin just clicked his tongue and went away.
"Okay I will not kill him but transport him to your headquarter and contact New Marineford to send at least some Admirals for transport as Kaido might interfere in this", said Kenshin to Smoker.
After that Kenshin told the straw hats to go to Dressrosa to save the citizen and come, Zou, whereas Kenshin will be taking Momonosuke and Kinemon directly. He also added, "Oh don't think if I am not there then you can slack off. If I don't see improvements then there will be very severe punishment" with a very scary tone.
Just after everything was cleared. Kenshin said to Aokiji, "Well since you are here, you wouldn't mind a little spar. Now do you?".
"Arara kids of these days sure lack respect aren't they", said Aokiji.
Hearing Kenshin, everybody was again surprised but was eager to watch the fight between two monsters. After everybody went to the ship to clear the area for them to fight.
"Let's start"
After that Kenshin raised his hands and sent a powerful attack using his word domain. Aokiji saw this and was shocked to see an invisible attack with his Kembunshoku Haki but still dodged it easily and retreated.
Kenshin kept on attacking after that till Aokiji reached outside of his domain. Aokiji saw the attack is not coming he said, "So, this is the range of your attack. What was that? Your devil fruit power or something else". Then he attacked using his ice devil fruit power.
"Ohh it is the Legendary level sword mastery", said Kenshin while cutting down and attack that was coming towards him. He was also using Kembunshoku Haki to check for any surprise attack as you can never be careless against this level of power.
"Oye Oye that's dangerous you know", said Aokiji but his attack power was slowly increasing. And Kenshin's sword domain was not able to cut off some of his ice arrows.
"That's really expected. I cannot win against such monsters without using my sword", said Kenshin. After that Kenshin took out his Izanagi sword and sent a flying sword attack towards Aokiji. This was more powerful than the previous attacks.
After that Kenshin rush towards Aokiji to fight in close quarters. Aokiji knew he can't win so easily either. He used his awakening power and all the island began transforming into ice. Without Akainu's power to stop his ice. The whole island froze along with the large area of the sea.
Kenshin dodged to the air to avoid getting his body freeze. Then he sent a flying sword attack using his techniques "Rising Demon". (Note all of Kenshin's strength that is shown after the time skip does not include ki. Using ki will improve his battle prowess by 10-20 times)
The sword attack was too fast for him to dodge, he sidestepped to dodged along with creating a huge barrier to block the attack. The strike came, destroyed the barrier and touched Aokiji's cheek.
After getting injured Aokiji completely changed, His face turned serious as if he is careless he might die. The marines and the straw hat were also amazed. Zoro and Sanji were watching this seriously as they knew they will have to train even more or they will be left behind.
Their fight continues like this for about 3 hours. In these 3 hours, the battle has become very serious. Kenshin was rushing to fight in close quarters. Aokiji using his ice devil fruit powers to send needles, arrow and many more towards Kenshin to blow him away.
And whenever Kenshin reached very close, Aokiji made ice swords and coated with haki and fight with Kenshin. In this fight, Kenshin has gauged Aokiji's strength. Aokiji is on par with him based on physical strength, has awakened powerful devil fruit, haki is about low Legendary level, sword mastery is low master level.
They fought with each other for another 2-3 hours before they finished the fight, everybody watching this was not bored at all because it is not often do they get a chance to watch to fight at this level. Everybody swore in their mind to train to fight like them.
Kenshin took a deep breath and said, "It is not going anywhere. I cannot improve any further than this by this battle. Let's finish it". To which Aokiji just agreed and they both stopped the fight. In this fight, Kenshin's major gain was that he stabilized his haki and Sword Mastery at Mid Legendary level and according to estimation when he will fight with Big Mom, wither his Haki or his sword mastery will improve to high Legendary level.
After the fight, Kenshin went to the ship and Aokiji went away on his bicycle.
"Kenshin are you okay?" asked his crewmates.
"Yeah, I am fine. We were just sparring and not trying to kill each other, so it's fine", said Kenshin.
"What!! you call that simple sparring. The island almost got destroyed and you both were fighting for more than 5 hours", said Nami while shouting.
"Calm down. I will rest here today and tomorrow I will take Momonosuke to Zou whereas you all will help bring his partner and help the citizen of Dressrosa if possible", said Kenshin.
"Okay but why are you giving the orders", said Usopp. Hearing this they all nodded.
"I will listen when Luffy will become strong enough to defeat me. Otherwise, you all will listen to my orders. And remember about the improvements to make when you will reach Zou otherwise there will be punishments", said Kenshin.
"There is one problem. We don't know how Kanjuro looks like", said Sanji.
"Hmmm that's sure is a problem", said Usopp.
"How about I only take Momonosuke and Kinemon will search for Kanjuro and come with you guys to Zou where we will decide our next plan", said Kenshin to which everyone nodded.
Similar to the anime the kid was truly a devil. He grabbed both Robin's and Nami's boobs while smirking towards the perverted trio (Brook, Sanji, and Kinemon).
The next day Kenshin grabbed Momonosuke and said goodbyes to the straw hats and went in the direction of Zou by running in the air.