Master Emerald (Sonic X)

The Master Emerald (マスターエメラルド) is an object that appears in the anime series Sonic X and its comic series published by Archie Comics. It is a massive, green emerald from a parallel earth and a powerful ancient relic, capable of controlling the Chaos Emeralds, that keeps Angel Island afloat; without it, the island will fall down from the sky. It is protected by its current guardian, Knuckles the Echidna.

When Knuckles was sent to earth, the Master Emerald was left unprotected until it came to Earth as well. During its time on Earth, the Master Emerald became a key factor in several battles until it was returned to its dimension. It would later be used as a vital power source for Knuckles and his allies' battle with the Metarex where it was sacrificed to save the universe.

Ancient Times
The Master Emerald's true origins are shrouded in mystery. The earliest documentations of the Master Emerald date back to the era when Tikal's tribe of Echidnas still thrived. In those times, the Master Emerald and the Chaos Emeralds resided in a sacred shrine in the Mystic Ruins where a colony of Chao lived peacefully, guarded by the mystical water beast Chaos. Eventually though, Pachacamac, leader of Tikal's tribe, set his greedy eyes on the Master Emerald and the Chaos Emeralds to obtain ultimate power and crush his enemies. When Pachacamac's daughter Tikal learned of her father's plans to raid the shrine for the Emeralds, she tried in vain to make the shrine's residents leave, but her compassion convinced the residential Chao to let her see the Master Emerald. As if the Master Emerald spoke to her, Tikal recalled an old mantra telling of the controller of the Chaos Emerald and it made her understand how it was that controller.

When the time of the raid came, Pachacamac and his warriors brought destruction to the Emeralds' shrine. Tikal attempted to stop her clan, but her pleas fell on deaf ears. Trampling over Tikal and the Chao alike, the Master Emerald and the Chaos Emeralds were left for the echidnas' taking until Chaos blocked their path. In a fit of rage, Chaos took the Chaos Emeralds' power and wiped out most of Tikal's tribe. With Chaos lost to rage and out of control, Tikal prayed to the Master Emerald with her mantra to stop Chaos, which the gem responded to by sealing Chaos inside itself along with Tikal so the female echidna could sooth its anger.

Following the Perfect Chaos incident, much of the Master Emerald's history is unknown, though it appears to have remained on Angel Island since then. Around present day, the task of protecting the Master Emerald was taken up by Knuckles the Echidna, a mission he would uphold with outmost seriousness and discipline.

Chaos Emerald Saga
When Knuckles was transported to earth by Chaos Control, the Master Emerald was left unprotected. During most of his time on earth, Knuckles was on an almost obsessive quest for a way back home so he could return to the Master Emerald. While no harm was done to the Master Emerald while Knuckles was gone, Angel Island and the Master Emerald were transported to earth by a giant Chaos Control triggered during a battle between Super Sonic and the E-99 Eggsterminator.

Chaos Saga
Following the Master Emerald's arrival on earth, Knuckles resumed his duty to protect it. Six months later though, the Master Emerald was shattered by Dr. Eggman to release Chaos, its pieces being scattered far and wide and causing Angel Island to fall into the sea. As such, Knuckles began searching for the fragments across various areas. Whenever Knuckles found a fragment, it would show him a vision of Tikal and Chaos' past. After Knuckles had brought most of its pieces together, the partially restored Master Emerald showed Knuckles that the remaining fragments were on the Egg Carrier. Not long after, Knuckles brought the final pieces back and fully restored the Master Emerald. When Chaos had finally been calmed down by Sonic, Tikal and Chaos returned to the Master Emerald to live in peace.

Shadow Saga
Shortly after Perfect Chaos' attack on Station Square, the Master Emerald was stolen by Rouge the Bat despite Knuckles' attempt to stop her and taken to Space Colony ARK. However, Knuckles followed her up to the ARK where Rouge let him take it back after he saved her life. When the Space Conoly ARK was send on a crash course into earth which would destroy the planet, Rouge had the idea of using the Master Emerald to deactivate the Chaos Emeralds that were current powering the ARK's descend. With help from Sonic, Decoe, Bocoe and Shadow, the Master Emerald was brought to the ARK's core where Knuckles called upon its power and shut down the Chaos Emerald.

Homebound Saga
When it came to light that the presence from everything from Sonic world were threatening to freeze time, the Master Emerald and all else not native to earth were send back to their world using a machine Tails Chuck Thorndyke had created.

Metarex Saga
Following the return home, the Master Emerald was peacefully protected by Knuckles on Angel Island over the next six months. At that point, the Master Emerald served as the power source for Christopher Thorndyke's crossover into Sonic's world. As a result of the time difference between Earth and Sonic's world, Chris physically regressed six years which were stored inside the Master Emerald, at least according to Eggman's theory.

As Sonic and co. prepared to set out to travel around the galaxy and battle the Metarex, an alien race of cyborgs bend on universal dominance, the crew took the Master Emerald from Knuckles to the Blue Typhoon, which Knuckles was forced to accept. Onboard the Blue Typhoon, Knuckles would call upon the Master Emerald's power in time of need, most importantly to power the Sonic Power Cannon, the ship's most powerful weapon. In the final battle against Dark Oak, the Metarex's leader, the crew attempted to use the Master Emerald's energy to destroy Dark Oak with an extremely powerful shot from the Sonic Power Cannon. However, this came at a terrible coast for Knuckles: the attack pushed the Master Emerald beyond its limit, leaving it shattered and powerless.

After defeating the Metarex, Knuckles returned the Master Emerald's shards to Angel Island where he could watch over them until it could regain its power naturally, though the process would take some time. The Master Emerald's destruction also meant Chris' age data was corrupted, preventing him from returning home through that method.