Cassandra Rayne

She was a Champion of the Powers That Be that fought The First Evil and could hurt it. But before The First killed her and hid her bodyparts in Sunnydale, Cassandra placed Hope's Dagger (the only weapon that can hurt The First) in The First's lair, a castle in it's own hell dimension. Cassandra guids Buffy to the castle where only a champion may enter. She dies again after Buffy's victory over The First.