top 5 who were both pirates and marines in one piece

#5 Koby

Koby is a Marine Captain who trained together with Helmeppo under Vice Admiral Garp’s supervision. He is currently a member of the Marine special forces unit SWORD. He was formerly an involuntary cabin boy for the Alvida Pirates until he was liberated by Luffy.

#4 Vergo

Vergo was one of the four elite officers. At age 26, he enlisted in the Marines under Doflamingo’s orders. Having spent 15 years ascending the ranks, he nevertheless was an enemy to the organization from the beginning, as he assisted Doflamingo in criminal activities by abusing the privileges as a high-ranking Marine officer, as well as passing off vital information and coverups. He was dishonorably discharged when Smoker reported him to Sakazuki

#3 Ceasar Clown

Caesar Clown used to work with Marines as their scientist. During the Dressrosa Arc, Donquixote Doflamingo declared Caesar to be his direct subordinate, meaning Caesar was a de facto member of the Donquixote Pirates. He also took part in a rebellion against Big Mom together with Fire Tank Pirates and Straw Hats.

#2 Donquixote Rosinante

Donquixote Rosinante was the younger brother of Donquixote Doflamingo. He became an Elite Officer of the Donquixote Pirates, serving under Doflamingo under the codename Corazon.
The truth, however, was that he was a Marine Commander, working undercover in order to stop Doflamingo. He was found out by the former Corazon, Vergo, and was executed by Doflamingo 13 years ago.

#1 Kuzan

Kuzan, better known by his epithet Aokiji, is a former Marine Admiral and the first one to be revealed. He was nominated by Sengoku for the position of Fleet Admiral. However, after losing the position to Sakazuki, he resigned from the Marines and affiliated himself with the Blackbeard Pirates. It is unknown what standing he has with the crew, but some like Jesus Burgess are not so quick to trust him because of his past as a Marine, but Blackbeard pays it no mind.

akainu has the most powerful devil fruit in one piece?

According to an interview with Eiichiro Oda, he stated that if Akainu were to become the protagonist, he is so strong that he could end the One Piece series within a year.

Akainu ate the Magu Magu no Mi, a Logia-class Devil Fruit which grants him the ability to transform his body into magma and manipulate it at will. The main strength of this Devil Fruit is that it allows the user to produce magma to attack their opponents with. The intense heat can vaporize an iceberg instantly and boil the seawater that the magma lands in.

Akainu’s ability is naturally of a higher order than Ace’s pyrokinetic abilities, as the higher heat and smothering abilities of his magma allowed him to successfully harm Ace despite Ace’s Logia-defense, and ultimately kill Ace due to this superiority.

The destructive heat and explosive power from the magma enables Akainu to cause massive damage, and to take people like ivankov and jimbei with minimal effort. 

During the decisive ten day battle on Punk Hazard for the position of fleet admiral, Akainu showed the furious power of his Devil Fruit as he changed the weather of one side of Punk Hazard and left it in a blaze. Because of this, many fans speculate Akainu has awakened his Devil Fruit.

"the level of admirals"

I've noticed that the term "admiral level" is always used when people are describing someone they think is lower than yonko, this is a form of downplay that seperates the admirals from the highest tier, where they truly are, alongside the yonko.

In marineford, we see the Admirals fighting on par with whitebeard, the strongest man in the world. Oda even showed us that whitebeard and shanks were equal standings when they clashed and the clouds split evenly. Even if you want to downplay whitebeard to the weakest yonko, he definitely still yonko's level. It's an extreme difficult fight for any of the other yonko to defeat him. Saying anything else is blasphemy.

the previous owner of gum gum fruit

The evidence i will provide is purely speculatative and hypothethical in the sory of one piece. Since the start of the series, a question that may have sat in the back of our mind would be who was luffy prodecessor of the gum gum fruit 

The solution I have found to work for the question, in which I speculate, would be that the specific devil fruit and its powers were once possessed by Portgas D. Rouge, Ace’s mother.

The purpose behind this would be the nature of Ace’s birth. The average pregnancy lasts around 9 months. The purpose of this would be based on the carrier’s body withstanding the pregnancy as well as the baby remaining healthy if possible. In the manga, it says that by the sheer force and will of Rouge, she was able to hold off Ace’s birth until the 20 month mark. By these standards, that would make Ace as old as an 11 month old child with the addition of the 9 month pregnancy. The average 11 month old baby weighs 21 pounds. The normal female human body would not be able to sustain a baby of that weight without abnormalities or powers.
think Ace had the extended pregnancy due to his mother’s Gomu Gomu No Mi powers. Her powers allowed her to stretch more than the average body, allowing her baby to have an extended pregnancy albeit, there were still consequences for the rather unnatural birth leading to Rouge’s death.

In a different perspective, this would also explain why Shanks would have the devil fruit. Knowing Rouge would have had some sort of connection to Roger, Shanks would have found the fruit to find a suitable user based on his relationship with his former captain (possibly Ace if Shanks knew about his birth/whereabouts)

As uncertain as we are of Shanks, most of us see him as a man of good intent. Based on this fact, I believe that Shanks had the devil fruit to use based on his good standing with Roger. The entirety of this speculation brings a full circle idea that connects Luffy to Roger’s life in a minuscule manner.

*Theory by Skills D. Kyle