SPOILER The Darkest of Dark Crystals

Cut to the chase:
Lightsabers are made with crystals.
Jedi use certain natural crystals, while Sith seem to use artificial ones.

Rumors state that Anakin's lightsaber (which Luke lost on Cloud City) holds the key to something huge in TFA, likely the tomb for the Uber sith (where Luke is hiding.)

Many people have speculated that Anakin's murder of Younglings with this lightsaber makes it more powerful in dark side energy. In essence, the greater the crime, the stronger the weapon becomes.

Following that logic, what if the crystal inside every Sith's lightsaber is the same crystal used by their predecessor? What if it's stolen once the last guy is murdered, then used as a way to boost the stats of the new guy/gal's lightsaber? A crystal that's been used for over a thousand years to do much, much worse than kill a temple full of Younglings would seem to be all-powerful.

Ride that train of thought to this station: Might the crystal inside Anakin's lightsaber have belonged to whomever is in the tomb, and that's why it's the key?

 

Thanks @walnutthewise

The big mystery is whether or not these lightsabers and crystals actually do hold great power. It gets even hazier when you consider these items could just have a psychological effect on whomever wields them... if a force-sensitive noob gets their mitts on one, they may suddenly believe they are all-powerful... which may or may not end so well. (I'm imagining the Kylo character falls victim to such overconfidence, and gets wrecked in the process.)

Basically it's hard to tell (esp. if we're talking about force sensitives) whether these items do anything outside of give someone a psychological boost, which then may open them up to their full potential. That potential may have been there all along.

 

Kira begs to differ.

 

Plot

A thousand years ago on the planet Thra, a magical crystal cracked, and two new races appeared: the malevolent Skeksis, who use the power of the "Dark Crystal" to continually replenish themselves, and kind wizards called Mystics.

Jen, an elf-like Gelfling taken in by the Mystics after his clan was killed, is told by his Mystic master that he must find the crystal shard, and that it can be found in the home of Aughra. If he fails to do so before the three suns meet, the Skeksis will rule forever. The Skeksis' emperor and Jen's master die simultaneously. A duel ensues between the Skeksis Chamberlain and General, both of whom desire the throne. The General becomes emperor and the Chamberlain is exiled. Learning of Jen's existence, the Skeksis send large crab-like creatures called Garthim to track him.

Jen reaches Aughra and is taken to her home, which contains an enormous orrery she uses to predict the motions of the heavens. Jen discovers the crystal shard by playing music on his flute to which it resonates. Aughra tells Jen of the upcoming Great Conjunction when the three suns will align, but he learns little of its connection to the shard. The Garthim destroy Aughra's home and take her prisoner as Jen flees. Hearing the calls of the crystal, the Mystics leave their valley to travel to the Skeksis' castle. Jen meets Kira, another surviving Gelfling who can communicate with animals, and her pet Fizzgig. They discover that they have a telepathic connection, which Kira calls "dreamfasting". They stay for a night with the Podlings who raised Kira after the death of her parents. However, the Garthim attack the village and Kira, Jen, and Fizzgig flee when the Chamberlain prevents one of the Garthim from attacking them. Most of the Podlings are enslaved.

Jen and Kira discover a ruined Gelfling city. Finding a relief with prophetic writing, Jen discovers that the shard, a part of the Dark Crystal, must be reinserted to restore the Crystal's integrity. The Chamberlain tells Jen and Kira that he wishes to bring them to the Skeksis to make peace, but they distrust him and refuse. Riding on Landstriders, the Gelflings arrive at the Castle of the Crystal, where they see the Garthim that attacked Kira's village. Kira and Jen unsuccessfully attempt to free the captured Podlings. Kira, Jen and Fizzgig infiltrate the lower parts of the Castle. The Chamberlain confronts them again and tries to convince them to make peace; however, the Chamberlain wounds Jen and takes Kira to the Castle. The General restores the Chamberlain to his former position. On the suggestion of the Skeksis' resident scientist, the General decides to regain his youth by draining Kira's life essence, recalling that its potency allows a Skeksis emperor to maintain his youth for longer periods than that of the Podlings on whom they have been forced to rely since the Gelfling genocide. Aughra tells Kira to call out to the animals imprisoned in the laboratory. They break free from their cages and the Skeksis scientist falls to his death, upon which his Mystic counterpart simultaneously vanishes.

The three suns begin to align as the two Gelflings reconvene in the Crystal chamber. The Skeksis arrive to prepare for the immortality that they will gain from the Conjunction if the Crystal is not restored. Jen is discovered and drops the shard, but Kira throws it back to him and is stabbed to death by the Skeksis' high priest. Jen inserts the shard into the Crystal, unifying it as the Mystics enter the chamber and the dark palace begins to crumble away and transform into a castle of bright crystal. As Aughra, Jen and Fizzgig watch, the Mystics and Skeksis merge into tall glowing beings, known as UrSkeks, one of whom says "we are again one", speaks to Jen of their history, and revives Kira. After leaving the Crystal for the two Gelflings to "make [their] world in its light," the UrSkeks depart, and the land is shown rejuvenated and the Castle transformed into a palace of crystal.