Devil Fruit

Devil Fruit (悪魔の実, Akuma no Mi), called Curséd Fruit (pronounced with two syllables) in the 4Kids English dub, is a mystical fruit that can give the eater many kinds of strange and interesting abilities depending on the fruit and its type. There are some seen only in the anime or only in the manga.

About
I once heard that all the Devil's Fruits are the Sea Devil's incarnations. If you eat one you'll gain a special ability, but you won't be able to swim.

— Shanks speaks to Buggy on Devil Fruits.

Devil Fruit are said to be the fruit of the Sea Devil and that the secret to their power is hidden in the Grand Line. Because encounters with them are rare (especially outside the Grand Line) a number of rumors about them have risen making it difficult to tell whether some things are fact or fiction. The average person knows nothing or very little about what they are. Because of their power, if sold they can expect to reach well over 100,000,000 and Devil Fruit users themselves are sold at market prices as slaves. There are more than 100 types of Devil Fruit.

One running theme with Devil Fruits, however, is the fact that they taste unimaginably horrible, to the point of making it seem like the eater had taken poison. The Devil Fruit, when consumed, gives the consumer a power or special trait though they won't immediately become aware of. They come in different shapes, colors, and all Devil Fruits have swirl marks on them of some kind. There can be only one of each type of fruit at a time. Only one bite is needed for the user to gain the power of a Devil Fruit, after which the Devil Fruit becomes a simple, useless, disgusting fruit. Swallowing the fruit whole, as Buggy did, has the same effect, peeling off the skin and eating it piece by piece also works.

Identification
We can figure out the name of a fruit by the power it gives, but the kind of power we get is completely up to chance. — Kaku on his and Kalifa's unidentified Devil Fruits.

There is a book in the Grand Line with Devil Fruits listed (although sometimes a Devil Fruit is said to had been unidentified). The most notable example is Blackbeard in his search for the Yami Yami no Mi. Catalogs and a book were also mentioned by Spandam and Sanji. Shanks and his crew already knew Luffy's Devil Fruit was the Gomu Gomu no Mi (Gum Gum Fruit in English versions) before he consumed it.

While it hadn't been yet explained how to acquire that knowledge, according to Oda in a SBS, the same power of a Devil Fruit can exist more than one time (but not at the same time). Spandam mentions briefly that Devil Fruits have an aura around them which can often help identify them and that the two Devil Fruits he supplied to Kaku and Kalifa contained an unknown aura.

Side Effects of Devil Fruits
With this new power comes a weakness: the sea rejects the new Devil Fruit user and they become helpless while submerged in water (or "becomes a hammer," in Japanese parlance). Oda stated in SBS that Devil Fruit users are susceptible to all types of water, not just seawater. He elaborated on this, saying that "moving" water, like rain or waves, does not weaken Devil Fruit users, while standing water does.

If a user is not completely submerged, they can still use their powers from the parts of their body that are above the water. This was demonstrated by Kalifa, who was still able to produce bubbles from the parts of her body that were not under her bath water (although, as stated by Nami, this had effectively cut her strength in half while in the water). However, if the user's body has been permanently altered by the fruit, then the user's ability can be manipulated by outside sources; i.e., when Luffy was knocked into the pool at Arlong Park, Genzo and Nojiko dove underwater and stretched his neck so his head would be above water. Being weak against the sea proves deadly to many Devil Fruit users who are pirates and Marines sailing the Grand Line.

Seastone, a special substance that emits the same energies of the sea, can also cancel out Devil Fruit powers through physical contact with the user. Depending on how much physical contact the users has with the Seastone, their movement may also be weakened.

One rumor, as recounted by Cipher Pol's Jyabura, is that Devil Fruits house actual devils that will fight when placed in proximity of one another. The resulting battle would destroy the users' bodies. Nevertheless, Blueno contradicted this claim, stating that Grand Line scientists have noted that the phenomenon of one's body destroying itself only occurs when one consumes two Devil Fruits.

Consequences of Consumption
It must be a horrible life if you get some weird power. Regardless of the type of power, it all depends on how you use it. The chances of you weakening from it are very low. Besides, being a hammer isn't much of inconvenience.

— Rob Lucci on Devil Fruit power.

The main attraction to eating a Devil Fruit is the powers bestowed upon the user with many spending their entire lives seeking out just one type of fruit. More often than not the power is far more useful than never being able to swim again. However, due to lack of information known by most, and with Devil Fruits still unknown, the average consumer plays Russian Roulette consuming one and there is no way of changing what power you get once consumed. With no way of removing the curse all Devil Fruits users are labeled as "freaks", "Devils", and "monsters" for the remainder of their lives. All Devil Fruit users have to be trained to a certain degree from simple activation control to full battle techniques.

Another problem with the Devil Fruits is that a few of them offer "weird" or "useless" powers. While many citizens can be fascinated by their powers, others may leave a consumer leading a miserable life full of discrimination from those around them. Certain societies who are blind to the existance of Devil Fruits usually are told lies regarding the reason behind their strange abilities, keeping secrets but commonly causing misconceptions on how this power was achieved.

You could sell 'em for hundreds of millions. But one bite might leave you with a lifetime of problems you know!?

— Jyabura's warning to Kalifa and Kaku.

Taking into account all of the devil fruits so far, there is yet to be a genuinely useless one besides the Hito Hito No Mi (which would simply "enlighten" a human consumer) hence it is likely that all devil fruits have practical uses.

Research
Doctor Vegapunk, a Marine Scientist, is responsible for the research into the effects of Devil Fruit and Seastone heavily. His research has also led him to devise the method that lets an inanimate object (such as a gun or a sword) gain the effect of a Devil Fruit (it has not yet been shown how this is done).

Tony Tony Chopper created, over five years, a drug called "Rumble Ball" that enhances the effects of the Devil Fruit. Thus far he is the only one so far shown to have consumed it. According to him the Rumble Ball disrupts the wavelengths of Devil Fruit forms. It is implied that the "Rumble Ball" will activate when consumed by any Zoan type Devil Fruit user albiet with different but slightly similar effects.

Types of Devil Fruit

 * Paramecia
 * Zoan
 * Logia

Trivia

 * Devil Fruit as expected, has been the center of several myths within the fandom due to fan Speculations.
 * In the original two pilots of One Piece, Luffy's Devil Fruit power, the Gomu Gomu no Mi, was the power of the Gomu Gomu tree that grew once every 50 years and there were no signs there existed other powers.
 * Many of the fruit names come from Japanese onomatopoeia and Japanese vocabulary.
 * Strangely, a Devil Fruit power also generally affects the clothes the user is wearing. Paramecia fruit users alter their clothes along with themselves automatically (for example, Luffy's clothes stretch to fit him, Mr. 1's pants legs become blades along with legs, etc.), Zoan fruit users' clothes will fit in the same proportions after transformation (Jyabura's shoes are considerably stretched when in the hybrid form), and Logia fruit users transform their clothes (and subsequent accessories) in their element along with them. The effects of Devil Fruit in clothing has no explanation, but resembles old comics (modern adaptations often bypass it) in which may be considered a logic error.