Yomi Yomi no Mi

The Yomi Yomi no Mi is a Paramecia type Devil Fruit which allows the user to come back to life after dying. The name is derived from Yomigaeru (よみがえる), meaning "Resurrection", also, Yomi (黄泉) is the name of the Japanese underworld. It was eaten by Brook. In the Viz Manga it is called the Revive-Revive Fruit.

Strengths and Weaknesses
The major strength of the fruit, as demonstrated by Brook, is that it gives its user another life after being killed. After death, the user continues to exist in whatever state they were revived as and can even go as far as to grant a form of "immortality" that lasts until the user suffers a second death. This of course is negated if the user's cause of death was drowning, and their body remains in the water. However, since the main attribute of the fruit is resurrection, the Yomi Yomi no Mi's power will remain dormant until the time when the consumer suffers his or her first death. As a result, until such time, the only aspects the fruit bestows upon its eater are the typical Devil Fruit weaknesses.

While the Fruit allows the user's spirit to once again return from the afterlife, it does not automatically return them to the physical body that it once resided upon during its mortal life. Thus, it is then up for the disembodied soul to search for the corporeal body in order to once again reunite with it. Though the user gains another life, their body however will continue being a lifeless corpse and will continue rotting away until the user's soul can find its way back to the body. When the user's soul returns to their body, the powers of the Devil Fruit will fortunately support the user's well being in the case that their body may be in a condition unable to support life.

While the fruit can make the user an undead being of sorts, it however grants the user the ability to still feel pain as proof that they have been truly resurrected back to life, regardless of what physical condition they've been revived in. This is a worthy note because this separates the power of the Yomi Yomi no Mi from the zombies created by the Kage Kage no Mi because though both powers work to make the dead come "alive" again, the Kage Kage no Mi zombies don't feel pain because they are not truly "alive" at all. Other than that, the user is still affected by the standard Devil Fruit weaknesses.

Brook demonstrated a new power of his Devil Fruit on Fishman Island after the timeskip. Brook's soul that came back to inhabit his skeleton is still able to leave the body, similar to astral projection, and move it everywhere he wants to, it can even pass through walls, similar to Perona's own astral projection power. When Brook is in spectral form, it mostly resembles his skeletal face (complete with the omega letter-shaped crack across his forehead) and engulfed in spiritual flames; it appears to be not only visible but also audible to both people and animals, since Zoro and Usopp were seen being able to converse with Brook while in this form, and Pappug was shown scampering away from Brook in this state, mistaking the skeleton's soul as a ghost, frightening the starfish. It is currently unknown as to how far the extent can Brook maintain this separation of his soul from his body, or if there are any limits about it at all (i.e. like when Perona uses her own spectral form, she leaves her corporeal body dormant). He discovered this power while praying during the time-skip and he used it to peek on women.

During his fight with Zeo, Brook reveals that in the past two years he has come to know the true power of his Devil Fruit. The soul of a human that died is supposed to be headed for the land of the dead but for his soul to exist in the human world it endlessly emits a powerful energy. The power that allows him to live in human world is not organs nor muscles, it is his spirit. He also shows that as long as his bones are not hurt any attacks will not go to his core like when Zeo beheaded Brook, his soul managed to repair it and connect his bones together again. He also shows that he can transfer this energy to an object like his cane sword in which he summons the chills of the other world. Lastly, he states that he can feel the souls of others.

Usage
While the fruit's only major bestowed power is only usable after death, its secondary powers however are rather useful in keeping Brook basically "alive". Through the fruit's powers, Brook is able to function without the presence of necessary and vital body parts that have decomposed long ago. He is able to interact with the environment around him without the presence of eye balls or any other sensory organ to aid him. He, in particular, retains his ability of speech despite his vocal chords and even his windpipe have long since rotted away. He is able to taste and digest food like any other normal living thing to sustain himself. Drinking milk in particular heals him as the calcium intake repairs any of Brook's bones that may have been broken in battle. Depending on the situation, Brook is also able to produce organic matter such as tears, fecal matter, and even blood from his nose despite not having any organs nor bodily liquids to produce such matter.

Brook is able to move and stand up without the presence of tissue and muscles to support him, as well as be capable of getting tired or worn down despite not having any of those factors to begin with. Due to the fruit's powers holding up and moving his light skeletal frame, Brook is given an extremely light body. He is able to perform seemingly superhuman feats such as jumping extremely high and running on water. These allow him to travel great distances and aid him in battle. However while his light body lets him be lighter than an average person, Brook isn't immune from sinking. Brook will still sink like any other Devil Fruit user when placed in water. In fact, while Brook can run on water, he cannot stay above it too long.

Being a skeleton animated by the fruit's powers also allows Brook to do things that most other people cannot do due to their need of tangible living tissue. Not only is he able to use his light weight to execute fast attacks, but his lack of flesh also allows him to execute attacks that would otherwise be harmful, such as shocking himself with electricity and becoming an electrically charged projectile. Due to the lack of organs, Brook is also able withstand some deadly attacks to a certain degree. For instance, he was able to withstand his skull being shattered to a certain degree and was also able to withstand having several of his ribs broken.

Also, due to the Devil Fruit powers allowing it, Brook also has the ability to store objects in his skull by opening it along its crack. While Brook is able to do these things because of his Devil Fruit supported form, he however can still feel pain, as well as fatigue. However, the fact that he lacks the actual organs means that Brook can fore-go most of the necessities required by humans (i.e. eating, breathing, etc.), having stayed up on his old ship for a long time with nothing to sustain himself with. Based on his own statements and comments from others, despite the lack of any muscles it appears that he is able to grow stronger through normal training. Though Brook is able to repair broken bones, it seems all growth functions have stopped. For this reason Brook puts a lot of effort into protecting his afro, since he would be unable to grow it again if it was cut.

After developing the ability to remove his soul from his body, Brook uses the intangibility to his advantage to peek at women, as well as escape imprisonment of any kind while contacting other people for assistance.

After two years of training, Brook has mastered the use of this Devil Fruit to the extent of knowing its true nature. He reveals that in order for his soul to remain here in this world, it produces an almost unlimited amount of energy. He has also mastered the energy his soul emits to the extent that he can reattatch his bones by using this energy such as when he is beheaded he then attched his head back with the help of this energy. Brook can engulf objects such as his sword with this energy and thereby summon the chills of the underworld.

Trivia

 * Brook's soul, upon returning to the mortal realm to search for his body, resembles a hitodama, a representation of the recently deceased commonly found in Japanese folklore and pop culture.
 * Although Brook's soul is yellow in the anime, it's color is white and light green in the manga.