Short answers, pulled from the story.
Ashley Riot is a government-sanctioned assassin and Riskbreaker who was manipulated by the Valendia Knights of the Peace to believe he killed his own family. He was framed for the murder of Duke Bardorba and became the prime suspect in a political assassination that never happened. He ultimately chose to carry Sydney Losstarot out of the collapsing city of Leá Monde rather than inherit the powers of the Dark.
An earthquake struck the town of Leá Monde two and a half millennia ago, destroying its golden age and leaving the ground unstable. The city remained dead for twenty-five years before the events of the game began. The catastrophe brought the chapter in Leá Monde's history to a close and allowed the Dark to take hold.
The Blood-Sin is a tattoo carved on the backs of those who bear it, serving as the key to the city of Leá Monde. Sydney Losstarot held the key all along, and the tattoo was an abjuration of the flesh carved during the Inquisition of the heretics. The key-bearer, the duke, was required to have a successor to prevent all from being lost.
Cardinal Batistum is the true antagonist of Leá Monde who sought immortality through the Dark. He intended to use the city as a vessel for immortality by trapping souls in purgation and yearning for life. The Crimson Blades acted under his direct orders to acquire the powers of the Dark for themselves.
Combat in Vagrant Story requires the precision of a rhythm game where Ashley Riot targets individual body parts within a spherical grid. Players chain different attacks known as Chain Abilities to achieve large combos and deal damage to the enemy. The Risk bar system forces players to balance aggression with caution as attacking longer lowers accuracy and defenses while increasing critical hit chances.
Vagrant Story was released in 2000 and was selected as one of Sony's Greatest Hits three years after its release. The game was later made playable on Sony's PlayStation Portable and PlayStation 3 consoles on the PlayStation Stores in Japan, Europe and North America. It has been referenced in Final Fantasy XII in 2006 and Final Fantasy XIV: Stormblood in 2017.