The English dub/original name of the stone used to bind the power of the Nether Realm. In both versions, this stone, a purple magatama rested in an ancient temple at the bottom of a lake. The reformed warlord Anubis/Shuten used the power of the Ancients/Kaos staff to reach it.
According to the character Badamon, the Jewel of Life is one of the three weapons that could destroy the Nether Realm. The Armor of Inferno, the Soul Swords of Fervor, and the Jewel of Life.
Though most of its powers are unknown and only a few have been seen in the show, the Jewel has the power to create a shield, blind enemies, destroy the spirits possessing soldier's armors, banish Netherworld priests, and for a short time, seal Talpa's power to keep him from defending himself against the final attacks of the Ronin Warriors/Samurai Troopers.
One considered use of the gem was to prevent Ryo from dying in the final attack when he was sucked into Talpa's body in the last battle. The Jewel came to life at the same time the Ronin Warriors went to attack Talpa and saved Ryo from being killed by his friend's weapons.
The Jewel took the place of the Ronin Warriors in the second half of the TV series as a means to protect Mia and Yulie.