Sae Krolis
The legendary 8th Rune of Ticondera, called the Hidden Rune because few ever knew of its existence. It is an object of unfathomable evil, said to be the very Heart of Darkness in ancient Ticonderan folklore. Such was its power that when Thanatos obtained it sometime around 23 WR, He was able to obliterate Tahran simply by touching Him with it, and also used it resurrected the Dark Goddess Tyr.
After Thanatos was defeated, Sae Krolis vanished. Its current whereabouts are unknown, though some speculate it's sitting in Praxer Riose's bathroom or some such.