Shichibukai

The Shichibukai (七武海 Shichibukai, literally meaning "Seven Military Seas"), the full title being Oka Shichibukai (王下七武海 Ōka Shichibukai, literally meaning "Royal Seven Military Seas"), are seven powerful and notorious pirates who have allied themselves with the World Government.

Overview
The Shichibukai is an organization of seven pirates turned privateers in the service of the World Government. Although they work for the World Government, the Shichibukai do not care about or respect the Government, or even other Shichibukai, and are often considered by the Marines to be no different from any other pirate. On the other hand, they are known as "government dogs" and are despised by other pirates, but are still feared and respected for their infamous reputation and strength before, and even after they become Shichibukai.

The Shichibukai seem to be a mixture of the more chaotic Yonko and the more orderly Marines.

Becoming a Shichibukai
A pirate may choose to join the Shichibukai if a space becomes vacant (which means that at least one Shichibukai must resign or be expelled from the group). However, in order for one to become a Shichibukai once this position opens up, one must be able to exhibit their strength against other pirates while choosing to pledge loyalty to the World Government (this ironically encourages pirates to gain infamy to become a Shichibukai) by making a pact with the Gorosei. If the pirate in question can be used as intimidation, the position may be offered to them, if no other pirate has accepted the position or proven to be more of an asset to the World Government. As expected, most members were already notorious pirates with high bounties, but even relatively unknown pirates can be admitted if they accomplish a feat to prove their strength.

Duties of the Shichibukai
They do not offer open opposition to the authority of the World Government, but are not obligated to follow its orders either. They are only allowed to attack other pirates and must also compensate the Government with a tenth of their plunder though this regulation is not usually followed at the very least. Each member of the Shichibukai must also have strong intimidation skills and a fearsome representation to put off others becoming a pirate and make them fear them. In addition, it can be assumed that once someone becomes a member of the Shichibukai they must be undefeated to maintain their position, or at least are not allowed to have a widely known debacle or scandal that affects their reputation.

Some of the members do various tasks for the government, such as conquering new islands for the World Government (described as "liberating") and guarding nations, but their ultimate purpose is to keep other pirates in check. Most importantly, the Shichibukai serve to help maintain the balance between The Three Great Powers.

Theoretically, the Shichibukai are allies of the government, and in times of war would collaborate with the Marines. Still, many Marine officers despise them and consider the Shichibukai to still be pirates.

Benefits
In exchange for these services, the Shichibukai are pardoned for their former actions and any existing bounties are rescinded.

As the Shichibukai are no longer outlaws, they can make money through legitimate business, as well as bounty hunting. Some, however, are content to simply float around the sea on their ships. The government does not seem to mind, and the Shichibukai are granted a great deal of autonomy in how they operate, at least thus far. Other benefits include access to resources normally out of bounds to normal citizens and pirates, such as the use of Kairoseki equipment.

Dismissal or Resignation
Even if they violate the law, the World Government and Marines may choose not to take any notice. Because of the risk involved with maintaining the three great powers, the Government tolerates the illegal activities of any Shichibukai and attempts to protect them if possible (or at least maintain their fame) though that is not to say that they would not dismis a Shichibukai for such actions. Dismissal from the Shichibukai holds not only the individual's loss of title, but in cases also the breakdown of possible politics affiliated to the Shichibukai.

Strength
The Shichibukai are a group of seven of the strongest pirates in the world and one of the Three Great Powers, the others being the Yonko and the Marines.

In terms of power, the exact relationship between the Shichibukai, Marine Headquarters and the Yonko is unknown. However, considering that these factions are stated to be in balance, the most reasonable conclusion is that each organization is approximately equivalent in strength. This, in addition to the fact that losing a single member of the Shichibukai can disrupt the balance of the world powers and cause distress to the World Government, indicates the extreme power each individual has. The strength of a Shichibukai is so great, that should they be imprisoned for any reason, they would be sentenced to Level 6 of Impel Down, the lowest and most secure level of the prison.

Because of their pact with the World Government, the Shichibukai are considered "Government Dogs" by other pirates. At the same time, they are also feared by them because all of the Shichibukai are insanely strong, each capable of destroying an average pirate crew on their own with no effort. They have such a fierce reputation that even other powerful and famous pirates are unnerved by them. Each member has some ability or power, the majority of which are Devil Fruit. In relationship to each other, it is not entirely known how they compare in strength.

History
None of the Shichibukai have appeared in the story so far.