Goethe’s Faust (inspired) AU
In which God bets with Mephisto that all his creations (humans and Mephisto himself) will eventually return to God, no matter how far they’ve strayed from him.
Mephisto, unwilling to have God taunt him, offers a deal to one of the immortal creations. He offers him to experience life as mortal, in return for his services after the human body has died.
The immortal, being curious about what life would be like as an ephemeral being, and wanting to know both suffering and happiness, agrees to the pact. Mephisto has him reborn as Moriyama’s second son. This time, he promises, that God’s creation will not return to the rightful path.