The Sovereign Rune is a heirloom of the Rugner family that is in the form of the Dragon King Sword. It is said that the rune came into possession of the Scarlet Moon Empire around the time of its founding, but the details are unclear.
The Sovereign Rune protects its user from all forms of magic, even that of magical coercion, such as the Conqueror Rune and the power of the other True Runes such as the Gate Rune. It also enables its user to possess the form of the Golden Hydra.
The fact that the Sovereign Rune was, in fact, the Dragon King Sword was a secret of the Rugner family, known only by direct members of the family line. As such, Windy did not know of the rune's location until Barbarosa revealed it to her. Its whereabouts following Barbarosa's leap from Gregminster Palace are unknown.
- Genso Suikoden Genso Shinsho Vol.14 (ISBN 4-7753-0217-5), page 66
- Genso Suikoden Kiwami Encyclopedia, page 84