I am the new Substitute Shinigami, Kanemoto Hisako, but my true identity is that of the East's greatest swordsman, Sasaki Kojiro. I have regained those sealed memories and powers when I was ran through by an unknown Shinigami's Zanpakuto, leading to my dramatic rebirth in death.
I rescued another mysterious Substitute Shinigami who goes by the codename 'Clarissa'. Because the real Shinigami hate Substitutes and are out to kill them, she tried to get me to give up my ambitions to pursue justice, but my resolve won out in the fierce battle that ensued.
After that fateful encounter, the Golden Witch bestowed upon me three treasures.
One is the ability to rule over death. (A Soul Candy pill named Chappy. It knocks my own soul out of my body and replaces it with Chappy; it allows me to transform without compromising myself. The rule for using this treasure is "only if someone is about to die.")
Two is the magical formula by which I can summon the Golden Witch to do my bidding. (She gave me her phone number. The rule for using this treasure is "don't call me when I'm at work.")
Three is all the lore in the Golden Land. (She told me what's really going on in the world. The rule for using this treasure is "don't tell anyone else.")
I should elaborate on the third treasure.
As I have always suspected, the world isn't as simple as it seems. Spirits wander the earth after their death, imperceptible to the eyes of most people... but not for mine! Anyway, the spirits can basically be split up into three categories: Shinigami, Hollows, and Pluses (regular ghosts). Hollows are the monstrous Bad Spirits that endanger the unlives and even the lives of everyone around them. Shinigami are like their opposites - they're the brave dark swordsmen that cleanse the world of their taint and also send Pluses off to heaven.