Moon Rune

History
The Moon Rune is one of the 27 True Runes. It governs over compassion and destruction. It makes its bearer immune to both conventional attacks and spells; rendering them nearly invincible. However, this power comes at a terrible price, as it turns its host into a vampire. Moreover, it dominates its bearer's mind until the person can gain mastery over its awesome power.

Sierra has been cursed by the Moon Rune for over 800 years. When she first got it, she ended up going on a killing rampage. She retreated into the forest to keep herself from harming others. As she gained mastery over this rune, she was able to tap into its powers of compassion, which diminished her vampiric impulses to drink the blood of the living.

The Moon Rune can draw power from the forces of the night or from a blood sacrifice of a hundred people. The Rune grants immunity to illness and immortality. The Rune also has a unique connection to the Night Rune given their similar sphere of influence.

Despite not possessing the True Rune for centuries after it was stolen by Neclord, it still recognized her as its "true master" when she and the others caught up with Neclord during the war. It obeyed her commands rather than his.

Sierra Mikain was and is once again the host of the Moon Rune. It's most notable previous host was Neclord.

Attacks
Despite appearing in Suikoden II, it could not be used. If it could, perhaps these would be the spells:
 * Waning Touch: Drains up to 200 HP from one enemy. Heals self for the same amount.
 * Crescent Wave: A crescent-shaped wave hits for 300 damage to all foes. 
 * Blood Moon: Drains up to 900 HP from one foe. Equally distributes that number as healing to party*
 * Eclipse of the Undying: Causes a lunar eclipse as undead creatures appear and attack all enemies for 1300 damage.

* Lv3 Spell: If you are in a party of six, each person would be healed 150 HP as the attack did 900 dmg to a foe. A party of three would be healed for 300 HP each.*