A piece left over after the Night Rune turned into a sword and split from the Sun Rune, the Twilight Rune is a unique rune and one of the three treasures of Falena.
Borne on the left hand, the Twilight Rune grants it's bearer tremendous offensive power. When used in conjunction with the Sun and Dawn Runes, the insanity that occurs with bearing the Sun Rune can be halted, and the power of the rune can be forcibly quelled.
The Sindar people used the power of the Twilight Rune, their western buildings were built with the Twilight Rune serving as a key. Although the eastern buildings and northern ones were not constructed specifically for the Twilight Rune, the Twilight Rune still can function as a key for them.
During the reign of the Queendom of Falena, the Twilight Rune was kept in the West Palace. It wasn't until the civil war would become more extreme between the Prince's faction and the Godwin faction that the Godwins would call upon it's power.
The first bearer of the rune was Alenia, a Queen's Knight loyal to the Godwin cause. The rune mistress Jeane is able to attach the rune to Alenia, but the woman cannot draw out the power of the rune. The Twilight Rune only allows people it chooses to wield it's full power. Realizing this, Gizel has the rune removed from Alenia.
The next person who would bear the rune is the sister of Queen Arshtat, Sialeeds. Unlike Alenia, the rune allows itself to be used by the princess. Sialeeds uses the destructive powers of the rune to great extent, destroying an ambush the Godwin forces prepared for the Prince.
Sialeeds was planning to destroy the main dam at Sol-Falena, which would, presumably, sweep away the Prince's army in a tidal wave. But the Prince sneaks onto the dam, only to be halted by a sight from Sol-Falena. Someone was using the Sun Rune. The power of the Dawn and Twilight Runes manages to curb that destructive power, but the strain is too much for the badly beaten Sialeeds, and the Twilight Rune passes to the Prince's bodyguard, Lyon.
Lyon uses the Twilight Rune in the northern ruins, and against the Sun Rune again.
After the end of the war, the Twilight Rune is removed and placed back on a magical bust. It is now kept by the Sun and Dawn Runes, rather then in separate palaces.