Shikon no Tama

The, also known as the Sacred Jewel or Shikon Jewel, is a powerful marble-sized jewel which grants whoever possesses it with immense power. Only a few, (such as Kagome Higurashi), can sense the presence, (or 'kehai'), of the jewel and its shards.

The Four Souls
The four souls described are from the of Naohi (直霊): Aramitama (荒魂, Courage), Nigimitama (和魂, Friendship), Kushimitama (奇魂, Wisdom) and Sakimitama (幸魂, Love). When a person contains these four spirits at their maximum, such as Midoriko, they unite to form a really strong and powerful balance within the soul that can be used for either good or evil.

Form of the Shikon Jewel
Physically, it is a sphere that appears to be made of some sort of crystalline material prior to the accident that shattered it. When purified, the jewel is a soft pink color, however the more tainted the soul and wishes of the person holding it, the more the color turns to a lurid black-violet. It is somewhere between a marble and a ping-pong ball in size when complete, but the shards of the Jewel of Four Souls are irregular in size and shape. It was created to be held by a priest, priestess or monk with exceedingly strong and powerful spiritual powers. However, to make it unhealthy it usually makes the host demonic and or not themselves.

Creation of the Jewel
The jewel had come into existence during the Heian Period of Japan by the battle of the great priestess Midoriko and a strong and powerful yōkai. She was able to seize the souls of yōkai and purify them, this power coming from having a positive balance of the four souls within her heart, and in a time of many yōkai ravaging the earth those who possessed spiritual powers such as hers were considered to be as powerful as one hundred samurai. Her spiritual power alone paled that of any other person alive, and it was said she could purify and destroy ten yōkai at once. Her final adversary and the one that claimed her life was created by many yōkai joined and anchored within the evil heart of a human who secretly lusted for her, similar to how Onigumo loved Kikyō and created Naraku.

After seven days and seven nights of fighting, Midoriko realized that she would be unable to fight off the yōkai, and as she was drawn into the creature's massive jaws, she seized the spirit of the yōkai and bound it within her own with the last of her power, killing both of them and creating the Shikon Jewel, which burst from her chest. Within the jewel, her soul and the souls of the yōkai she bound within it still battle on. The state of this battle is influenced by the person who possesses the jewel.

History of the Jewel
The jewel was controlled by various humans and yōkai for several centuries until it ended up being rediscovered by Sango's grandfather in the centipede yōkai, Mistress Centipede. The Yōkai taijiya (demon slayers) entrusted Kikyō with the guardianship of the jewel due to her purifying powers, but it leads to her untimely demise. Naraku deceives Kikyō and Inuyasha, who had fallen in love with her, into hating each other by making them believe they had betrayed one another. The purpose of his plan is to steal the jewel and corrupt it with their hatred and bitterness. Inuyasha is sealed to a tree for fifty years, and Kikyō is killed by Naraku, although she believes Inuyasha is responsible for her death.

This fate may have been brought about by a curse from Tsubaki, who proclaimed that should Kikyō ever fall in love, she would lose her powers as a priestess and have an unnatural and untimely death.

It is also notable that, since the jewel was created, no good wishes have ever come from whoever possessed it. Since many people desire the jewel, it only causes despair and danger to anyone who possesses it.

Overview
While shards of the Shikon no Tama empowers the user's whole body, it seems to be most concentrated to body parts where it was embedded. Examples being Kōga's legs, which enabled him to run at high speeds for long periods of time and Bankotsu, being a lot stronger physically from embedding jewel shards into his arms.

Specific Powers Granted by Shards

 * Animating a severed head: (Shibugarasu)
 * Using the Bone-Eater's Well: (Kagome, Yura)
 * Possession: (Tsukumo no Gama, Tsubaki, Kagome via Hari/Failed, Kagome via The Infant/Failed)
 * Enhanced Powers/Strength to both persons and objects: (Hiten, Manten, Spider Demon, Bankotsu, Kōga, Banryū, Tessaiga, Sacred arrows, Tsubaki)
 * Bringing inanimate objects to life: (Noh Mask, Kōtatsu's ink, Ninmenka)
 * Turning animals into demons: (Weasel Demon)
 * Bonding a human arm to a demon body: (Sesshōmaru)
 * Making docile demons become vicious/insane: (Rōyakan)
 * Relieving pain/being unable to detect reopening wounds: (Sango)
 * Prolonging Life: (Kansuke)
 * Resurrection of the Dead: (Kohaku, Band of Seven)
 * Infecting one of Kikyō's souls in order to control her: (Naraku)
 * Super-speed: (Kōga)
 * Making skin hard as stone: (Tōkajin)
 * Healing wounds: (Kansuke, Mōryōmaru)
 * Prolonging the switch between split-personalities: (Suikotsu)
 * By-passing/breaking seals: (Yōmeiju, Menōmaru)
 * Creating "incarnations": (Naraku)
 * Transformation into stronger forms: (Mistress Centipede, Shibugarasu, Naraku)
 * Staying alive despite bodily destruction: (Naraku)

Wishes Made on the Jewel

 * Wishes made by Kikyō:
 * To make Inuyasha into a full human and live together as ordinary people. (Unfufilled)
 * To see Inuyasha again. (Fulfilled)
 * To no longer fight. (Magatsuhi sealed her reincarnation's powers)


 * Wishes made by Naraku:
 * To have Kikyō. (Unfulfilled)
 * To have himself and Kagome replace Magatsuhi and Midoriko as the battling spirits within the Jewel. (Partially fulfilled, before the Jewel was destroyed)


 * Wishes made by Kagome:
 * The jewel's destruction. (Fulfilled)

Events during InuYasha
The jewel was burned with Kikyō, but returned fifty years later through a reincarnation of Kikyō's soul in Kagome, coming back from the future because of the jewel's power and the interference of the yōkai, Mistress Centipede (Mukade Jōrō). Kagome eventually unsealed Inuyasha, however, the jewel was lost to a carrion crow. While attempting to retrieve it by shooting the crow with an arrow, Kagome accidentally shatters the jewel into hundreds if not thousands of shards (Shikon no Kakera) which scatter themselves across Japan. Inuyasha's group (which includes Miroku, Kagome, Shippō, Kirara and Sango) are attempting to collect the shards and stop Naraku from getting the jewel for himself. When the Jewel was completed and Naraku had been slain, Kagome was absorbed into the jewel to start a new battle between good and evil.

Inuyasha followed her in and finds out that the jewel is trying to make Kagome make a wish so it can start the battle all over again. Because unlike most beliefs, Midoriko is still alive and fighting the demons within the jewel. The jewel wants Kagome to take her place and replace the demons with Naraku instead. Kagome finds out that the jewel does not really grant one's true wish. She realizes that Kikyō wished to be with Inuyasha and Naraku's wish probably wasn't an evil one as he had intended it to be. She remembers her grandfather telling her that the Shikon Jewel can only be purified by one soul that wishes to save everything. It's then that Kagome realizes the wish and makes it after Inuyasha joins her side.

In the manga, most likely Naraku/Magatsuhi's desire had dissolved forever Midoriko's soul to prepare the place for Kagome, because she come to help Inuyasha against the demons but then disappeared and never returned. Magatsuhi and Naraku were clearly destroyed forever by Inuyasha when he cuts the point of light in the darkness inside the Shikon Jewel with Meidō Zangetsuha and arrives in the Meidō outside the Jewel to save Kagome. This point of light, left by Kikyo before dying, was the key to kill Naraku and destroy the jewelry evil. In fact, with Inuyasha's attack, the Jewel's shimmering completely stops. The rest of the Jewel breaks and then disappears when Kagome makes the right wish for it to be taken out of existence.

Instead, in the anime version, Kagome wishes for the Shikon Jewel to be gone forever, thus freeing Midoriko's spirit so that she can pass on to the afterlife; Naraku is shown to have awakened and finally is content by the warmness that the Shikon Jewel shined as it is destroyed. Three years later eighteen-year-old Kagome returns to the past in which she lives with Inuyasha by her side every day as long as she could.

Trivia

 * It was voiced by in Japanese, and  in English.
 * In total Inuyasha's group collected 13 jewel shards before they were stolen by Naraku. (Miroku collected three on his own before giving them to Kagome).
 * Naraku collected all but thirteen of the shards on his own; the first ten collected by Inuyasha's group were given to him by Kikyō while he stole the remaining ones to complete the jewel.
 * The Shikon Jewel is said to be able to turn a half-demon into a pure human or demon, though this has never been proven.
 * Unknown to Kagome and everybody else for that matter until the Sacred Jewel was retrieved from her body, she is the reincarnation of the dead Kikyo. She was born because of the jewel. When Kikyo laid dying and being cremated, her grief over Inuyasha's betrayal and her unresolved feelings for him carried the jewel and Kikyo's soul to the modern era, giving birth to Kagome. (It is also worth saying that this is the reason why she can travel to the Feudal Era, but only if she has the entire or a shard of the jewel.)

Reference
Shikon no Tama Perla de Shikon Камень четырех душ Esfera dels Quatre Esperits A Szent Ékkő Shikon no Tama Ngọc Tứ Hồn 四魂之玉