About six hundred years ago, a catastrophe-class monster attacked the Eastern Empire of Izanagi.
It was a massive, bird-shaped creature—hundreds of meters long and dozens of meters tall.
The attack resulted in the deaths of hundreds of thousands, and the empire was nearly brought to ruin.
Then, from the shadows, a mysterious man appeared and slew the monster with a white dagger etched in gold.
After defeating it, the man vanished without a trace, as if he had never existed.
However, the dagger remained—still embedded in the corpse of the monster. The emperor of that era ordered his soldiers to retrieve it and named it Shinketsu, meaning "True Blood."
The name was not without meaning. The dagger was said to possess the power to absorb anything it pierced—including the blood of the slain catastrophe-class monster.
The dagger was carefully kept in the treasure vault of the Eastern Empire of Izanagi for two hundred years.
