Everstone

The Everstone is an ancient magical cube of stone once used by the Forever Knights. It appears in Ben 10: Heroes of Evolution.

History
The Everstone was used to store supernatural energy inside it. Its magic was said be usable only by the Forever Kings, but was shown to release violently when the stone was broken.

The stone was said to be one of the tools the Knights never used. It was recovered following the Knights' eradication and used as a museum exhibit.

Former King and museum curator Phil Stephens hired knights Percy Lancaster, Simon Williams and Rick Thomas to steal the Everstone from Bellwood National Museum so Stephens could give it to his anonymous employer for further use to serve unknown intentions. The robbery was successful and the stone was kept inside a secure location guarded by Rick.

After Percy and Simon were apprehended, Rick was informed by Stephens, going under the digital alias "Kingston", to bring him the stone secretly at Bellwood Northwest Airport, an abandoned site used as an open airfield free for use. Stephens killed Rick, but he too was killed when a group of guerrillas blew up his plane along with the Everstone, whose energy violently broke out and sent blue electric energy and fire everywhere.

The guerrillas were killed by an assassin working for Stephens' employer, who let the incident slide and decided to use an alternative strategy.