Suikoden II takes place years after the events of the original Suikoden, and centers around an invasion by the Kingdom of Highland of the City States of Jowston. The player controls a quiet protagonist whose name is chosen by the player; he is the adopted son of Genkaku, a hero who saved the City-State of Jowston in a war against Highland years ago. The protagonist and his best friend, Jowy Atreides, each gain one half of the Rune of the Beginning, one of the 27 True Runes of the Suikoden setting, and become caught up in the intrigues of the invasion and the dark fate of those who bear the halves of that Rune.
The bearer of the Moon Rune and the Coven Mistress of Village of the Blue Moon. She is searching for Neclord, a rune-using vampire and former ally of the sorceress Windy. She appears also in Genso Suikogaiden Vol. 1 - Swordsman of Harmonia.
Sierra inherited the Moon Rune in an unspecified event over eight hundred years ago and is the original vampire of the Suikoden world. Overpowered by the rune, she succumbed to feeding off of other human beings to quench her unsatiable thirst for blood. To escape this fate, she left the world behind and retreated into a forest and took refuge in an abandoned residence. As other people wandered into her forest to commit suicide, she ended up granting them immortality with the rune and formed the Blue Moon Village. The village thrived under the rune's protection until it was stolen by Neclord; the villagers became demonic and Sierra, unaffected by the rune's loss, was forced to hunt them down. She meets Nash Latkje during a hunt for Rean Penenberg, the first person Sierra transformed into a vampire, and ends Rean's life with Nash's help.
Sierra leaves Nash and proceeds to Tinto after hearing of Neclord's presence there. With the help of Viktor, wielder of the Star Dragon Sword, and vampire hunter Kahn Marley, she is able to defeat Neclord and recover the Moon Rune.
It is speculated that after the events of Suikoden II, she marries Suikoden III's Nash Latkje. If Nash is given Sierra's (or the Narrator's) role in the Suikoden II "play" put on by Nadir, he sarcastically refers to himself as "Old Hag Sierra" and says that "I'm arrogant, never keep promises, and suck people's blood at any chance." Nash also claims to Chris Lightfellow that he's married and that his "missus" is quite a handful. Both of these instances are consistent with their relationship as portrayed in Genso Suikogaiden.