Moon Rune

The Moon Rune (月の紋章, Tsuki no Monshou) is one of the 27 True Runes. It is the rune of Sierra Mikain.

Suikoden
The Moon Rune is the rune of Sierra, the first vampire. It's unknown how Sierra found the rune but it seems to have strong side-effects seeing as Sierra became mentally unstable after inheriting the rune. The rune grants the magic of eternal youth to the bearer but at the expenses of the desire to feed on human blood, transforming those who are fed on into vampires. However, the rune also gives compassion to those same creatures, curbing their desires.

In the past, the Moon Rune was enshrined in the Blue Moon Village, giving energy and comfort to its inhabitants until the rune was stolen by Neclord. The villagers, other than Sierra, were then forced between feasting on blood to survive or a painful death. Neclord travelled the world with the rune, killing maidens and destroying villages but during the Dunan Unification War, he was defeated.

Sierra reclaimed the Moon Rune from Neclord before his death and continues to carry it.