Minato: I will sacrifice myself to seal the Kyuubi
Death: No, you don't!
The first order of business after becoming a Shinigami was to harvest Minato's soul, and then because of a moment of soft-heartedness, he was sucked into Minato's body, and the story ended up being assimilated with Minato. Minato is still Minato, the real protagonist, but because he has assimilated to the time-traveling Shinigami, he has an extra memory that does not belong to this world, and a memory of the future of his own world.
The time-traveling Death has become Minato's most powerful cheat in the future.
