He Who Fights with Monsters

1. To claim territories, players must kill the anomalies and boss in each; the center holds the birthing tree. Jason frees the young messengers in his territory and refuses to use them as combatants. Allies are scattered (Rick, Clive, Sophie, Farrah, Neil, Belinda), while claiming territories makes most people paranoid. Neil and Dustin find the rabbit man Jason subconsciously created with Healer's gift, whom Jason names Nik.
2. Boris Ket Lundi manipulates the corrupted gold-rank messengers and tricks Garth, High Priest of Undeath, into using a messenger heart that explodes, destroying Garth. The Undeath avatar cannot be killed, so Jason sanctions it: he draws its authority into his soul and begins converting it to Death authority, and almost loses himself. His friends fight the representation of Undeath inside him, and Farrah calls him back by shouting that Vehicle Voltron is the best Voltron.
3. Gary can stay in Jason's soul realm and die slowly, or bind to the natural array forever. He chooses to let go. The tree is a blend of the natural array, the incomplete birthing tree and the Soul Forge, and has gained a soul. Jason offers it life instead of fighting, and it becomes a forest in his astral kingdom with a nascent Voice of the Will, later named Arbour.
4. After the zone reforms and its barrier drops, Jason gives the god Undeath what remains of his corruption, builds a cloud city for the brighthearts, and removes the Builder cultists' star seeds. Velius and Raythe explain the Sundered Throne and ask him to repair it, which will turn his soul into a battlefield. He says goodbye to his friends, Gary reforges his sword into a transcendent artifact, and Jason steps into the nebula void as his mortal body dissolves.
5. Inside his soul, Jason sets up 'Rumble in the Jungle', a road across a jungle where the Great Astral Beings fight in mortal bodies. Whenever he dies, a sliver of his will slips into the forest and joins the whole. Years pass: Gary dies, Emi reaches iron rank, Team Biscuit grows, and the World-Phoenix kills Jason in the road while the Asano clan evacuates into their astral spaces.

After two years walking the road, the World-Phoenix and the Reaper find Jason emerging from the forest: he has been killed more than 100,000 times, with each sliver of will hidden in the forest and used to repair the Celestial Throne. He lets both Great Astral Beings go out of mercy and for Shade, then enters the nebula space with his four Voices of the Will, where the named Great Astral Beings arrive in their prime vessels, and sits on the Cosmic Throne. Every being who has or could have essences sees the message: 'Don't Panic. Everything is going to be fine. Welcome to the System.'

Gold rank: Jason's domains shine with golden light for a day when he reaches it (TV Tropes recap; Book 12 sheet confirms Gold).