When Little Oars went down Whitebeard was very sad. He was very angry when a giant Vice-Admiral said, "caught you off guard Whitebeard. You shouldn't have mourned in between the battle" and attack Whitebeard from the corner.
Whitebeard didn't even look at the giant and punched at the incoming attack using his devil fruit powers. The ax of the giant broke. He wasn't even given any chance when Whitebeard pulls the giant from his collar and used a quake power to destroy the metal helmet the giant was wearing. After that Whitebeard threw him away with a single hand like a rag.
Kenshin who saw Vice-Admiral Ronse's attack moved to the sides as he didn't want to get caught in the middle by an angry dad. With the ease with how Whitebeard decimated a Vice-Admiral shocked everyone. They realize that Whitebeard is not just a legend of the past, he still is a powerful Yonko.
Kenshin thorough, "Is Vice-Admiral Ronse brain dead, he could have silently attack Whitebeard if he wanted to attack. What's the big idea of announcing himself before attacking".
After that Whitebeard shouted, "Men use Oars body to move forward". After that Whitebeard pirates used Oar's body to climb up the plaza where they started the battle.
Boa Hancock also moved to attack, she used her devil fruits power to attack randomly, be it pirates or the marines. If anyone asked her then she gave a ridiculous answers "Because I am beautiful".
Elsewhere Doflamingo was using his strings to control the 10th Commander of Whitebeard pirates to attack his own crew-mates and watching them kill each other in pleasure.
Very quickly Allied pirates with Whitebeard used the path opened by Oars to go inside the bay area and fight with the marines. Very quickly marines have also begun pushing their plans forward.
After a few minutes, everyone noticed something falling from the sky. Marines thought it must be a Whitebeards attack and Whitebeard pirates also thought it must be marines secret attack.
But when they saw it clearly, they saw a marine ship with Rookie Strawhat Luffy, former Schichibukai Jimbei and crocodile, revolutionary Ivankov and many other convicts escaped from Impel Down. Every soldier from the Navy was shocked by this strange but powerful lineup.
Luffy who is known for his notoriety got much attention from marine Admirals, Schichibukai's ad well as Whitebeard pirates who know him as Ace's little brother.
Crocodile who saw Whitebeard suddenly got angry and rushed towards Whitebeard to strike him. Whitebeard and Kenshin ignored it as they also saw Luffy coming towards Crocodile. Luffy stopped Crocodile's attack and then some Whitebeard pirates came and circled around Crocodile if he attacks.
Whitebeard looked at Luffy's straw hat and said, "Brat the straw hat that you wear closely resembles the straw hat that once 'Red Hair Shanks' used to wear".
"Oh, old man you know Shanks? Yes he gave this hat to me for safekeeping", said Luffy.
"Did you come to save your brother", asked Whitebeard.
"Yeah. That's right", said Luffy.
"Do you know who you are messing with? A squirt like a squirt will be dead meat", said Whitebeard.
"Shut up! That not up to you to decide. I know what you are up to. You wanna become the King of the Pirates, right? BUT I AM THE ONE WHO WILL BECOME THE PIRATE KING", said Luffy.
Every marines and pirate alike were shocked. To say such words before the 'Strongest man on the planet' either require guts. Kenshin was watching from the sidelines laughed at Luffy's funny and ambitious introduction.
"How saucy you are. I won't forgive you if you cause me to trouble you spoiled brat", said Whitebeard.
"I am gonna do as I like. I am gonna rescue Ace", said Luffy.
Luffy then turned towards Kenshin who was sitting as if enjoying a show and asked, "Are you also from the old man's crew?"
"No", Kenshin replied with a smile as he knew what the next question is going to be.
"Then join my crew", said Luffy.
"No", said Kenshin.
"Okay after saving Ace we will look for all of our crewmates", said Luffy.
"But I didn't agree", muttered Kenshin. Kenshin knew Luffy's character so he didn't say anything and just watched the battle. Whitebeard saw Kenshin's situation and laughed which caused him a glare from Kenshin.
"We can punish all of them by death, can't we, Sengoku-san?", asked Kizaru.
"Absolutely", Sengoku replied.
After that Luffy told Whitebeard about the information that he received earlier to which Whitebeard thanked him. Hearing their conversation other who escaped from Impel Down were shocked as to how Luffy was talking with Whitebeard in a tone as if they were equals.
After that Luffy confidently charged towards the marine soldiers. Seeing these other commanders who were at the back rallied together and followed Luffy's trail and charged at the marines.
After some time Marco came and told the same information as Luffy. Marco said that he will help others who were tied by Vice-Admiral. To which Whitebeard said Marco to wait as it could very well be a part of their plan otherwise they(pirates) wouldn't have known about it so easily.
Luffy and the pirate behind them were rushing forward with great momentum until Kizaru came which forced many to pause but Luffy being a blockhead he is rushed towards it. It was Invankov's timely save otherwise Luffy would have been seriously injured.
Kenshin just sighed at Luffy's idiocy, then turned around to see Buggy who was saying something and the prisoners from Impel Down were understanding another thing causing them to revere Buggy. Kenshin just laughed at their charade.
Ivankov was about to help again but Kuma came and engaged in a fight with him. After that Luffy again like a blockhead and met with Fullbody, Django and Hina but easily evaded them and run forward fighting with many marines.
Luffy ran into Moria but was saved by Jimbei who use seawater to immobilize Moria's zombies. Ace saw Luffy getting bruised so he shouted at Luffy to go back and he didn't need Luffy's help to save him. But Luffy just said, "I am your brother and I don't give a damn about Pirate rules".
Luffy just said a sentence but it caused panic in the marines as they thought Luffy is also Pirate King Roger's son. Seeing them panicked Sengoku shouted.
"What are you doing? Don't let this rookie take control of the war! He is another loose cannon. He grew up together with Ace as his stepbrother and he is the biological son of revolutionary Dragon"
This shocked many people as they didn't know about Dragon's son and moreover he grew up with Pirate king's son as his stepbrother.
After that Whitebeard used Buggy's reverence within the prisoners to use and make them fight with the marines. Kenshin was having a hard time controlling his laugh looking at Buggy boasting whilst crying.
After that battle continues and almost all the allied pirates with Whitebeard have entered the bay area to battle with the marines. Whitebeard then orders DeCalvan brothers to take some pirates and drown all the ships that are coming from behind.
After that Luffy and the gang of pirates who were running forwards were again intercepted by Moria but Jimbei's used Fishman Karate to easily defeat him. After that Luffy was beaten by Smoker to which Boa Hancock came to the rescue and gave him keys of Ace's lock.
After that Luffy came across a few more obstacles but he was helped out by Whitebeard Pirates. But soon Hawk-Eye Mihawk came to obstruct him as he was interested in Luffy's ability to gather allies and he believes that it is one of the most dangerous in the world. (like Naruto's Talk no Jutsu).
Mihawk sent a flying sword attack towards Luffy which injured him but still avoided getting seriously injured. Jimbei tried to save Luffy but got injured by Mihawk instead. Luffy barely dodged two attacks from Mihawk.
After that Mihawk sent another attack horizontally which Luffy dodged due to his super-humans reflexes. But the Horizontal Flying Sword attack nearly cut down the frozen tsunami which was of the size of a mountain.
Kenshin's eyes lit up upon seeing this. In these 3 months, Kenshin's martial arts/ swordsmanship/ Haki all of them were at a low Master level. And Kenshin tends to improve his Haki and swordsmanship by fighting stronger opponents.[All of Kenshin's Haki be it Kenbunshoku, Bushoshoku or Haoshoku all of them are at low Master level. The details about gradation are written on chapter 27 author's note]
Kenshin saw how Mihawk was toying with Luffy to see where Luffy's fate will go. Kenshin knew that Mihawk was just intrigued by Luffy's plot armor ability. So he just sits there and watches the battles.
Kenshin also noticed that Mihawk hasn't used his Haki or sword mastery beyond the Master level (Mihawk has peak Grandmaster level sword mastery and Haki also in Grandmaster level) otherwise Luffy and Buggy would have been dead. But in the meantime, Luffy was again saved by Vista, another Whitebeard Pirate.