The Soul Eater, also referred to as the Cursed Rune, was inherited by Ted, survivor of an attack on his village, the Village of the Hidden Rune, some 300 years prior. The rune's power would be used by Ted on Mt. Seifu, which alerted Windy to his presence. Attacked and wounded, Ted managed to pass the rune onto McDohl. The rune is said to have power over life and death.
Windy wanted the rune so she could use it in conjunction with her own Gate Rune to take her revenge on the world. Said to be cursed, the rune is sometimes credited with causing wars and stealing the souls of those close to its bearer in order to increase its power. In fact, Ted declared its very intentions to be malevolent.
The grief it causes in its bearers is said to be the source of its power and it has been speculated that this in turn gives 'life' to its bearer, hence its name. There are also theories that the rune will eventually consume the souls of its bearer, but the truth behind this is unclear. These fears led to its epitheth as the Soul Eater.
The Soul Eater would continue to maintain some sort of connection with surviving past bearers. Ted was able to command the rune to take his soul even when the rune was borne by McDohl. It also appeared to weaken the effects of other runes in some fashion.
Leknaat cautioned against the use of the Soul Eater even at the last battle when she was unable to remove all of Windy's 80,000 strong monster army by herself. Following the defeat of Barbarosa Rugner Windy made a final attempt to seize the Cursed Rune but was rebuffed by the Soul Eater itself.
McDohl continued to bear the rune when he left the Toran Republic following the end of the Gate Rune War. Part of his motivation for leaving was his concern that the rune would bring further misfortune to those around him.
After leaving, he would try not to use the rune, fearing its power, but would be persuaded to do so in order to rescue Ko, a boy from Banner Village who fell into danger. Following this, McDohl would deign to use the rune on occasion for the New State Army's cause.