Defiance of the Fall

1. Abbot Peace and the monastery summon the Lotus Emperor's reincarnation, 84th Fatty. Abbot Peace gives Zac a Karmic tool to deal with the Great Redeemer. Fatty then leaves, taking the monks inside his inner world, and Zac earns the limited title Frontrunner and uses the tool to destroy a Karmic object of the Great Redeemer.
2. In the Underworld Zac disguises himself as Mr. Black, a wandering Undead warrior. Smaug (Hassan), head of the first big faction, attacks, is beaten, and signs a 500-year servitude contract.
3. Zac forms an Underworld Consortium to control its wealth (shares 50/10/25/10/5 between Zac, the Academy, the Demons, Verana and Calrin), frees a Union slave camp, removes the Union leadership, and meets the Underworld Council.
4. A grinding trip gets Zac to level 60 Undying Bulwark. He kills the Battleroach King for the Profane Seal skill and finds the roaches were a Technocrat experiment. Zac destroys the Technocrat Incursion at nearly the cost of his and Ogras's lives, and Hardness reaches High.
5. On the surface, the Port Atwood army is forced into a multi-day fighting retreat as the zombie hordes jam its teleport arrays. Half the army dies before Zac arrives, and Alea's soul is shattered by assassins sent by the Lich King Adriel. Zac smashes the horde and sends Alea home to a stasis array.
6. Void's Disciple, the Dominator leader, meets Zac and offers help against their common Undead enemy. Zac, as Mr. Black, then takes out four more Underworld Incursions in five days, reaching level 73 Undying Bulwark.
7. Zac ends the last Incursion in the Underworld, the Fire Golems, with the Council. He takes down a Birdman Incursion on the surface. Kenzie works out how to release the Origin Dao from the Dao Funnel, and Zac keeps the Funnel for his people. Seven people die, eight enter comas, and many break through.
8. Zac fuses Sharpness and Heaviness into the Fragment of the Axe and reaches level 75 Undying Bulwark. He and Ogras then take the System's token to the Tower of Eternity, where they offend the Tsarun, meet Galau (who hires them to carry him up) and attend auctions.
9. Zac kills Rasuiel Tsarun after being manipulated into attacking, taking his first spatial ring, a Prajna Cherry and a Pathfinder Oracle Eye. Catheya Sharva'Zi smells Draugr on Zac. The System puts a one-Tower-level bounty on him, so he, Ogras and Galau flee upward. They clear the first three floors in 13 days, with Zac fusing Rot and Hardness into the Fragment of the Coffin.

Zac and Ogras are on level 28 of the Tower (the top of the third floor), with Galau staying on level 31 to make Nexus Coins. Back on Earth, the Undead and the Church have teamed up to attack Port Atwood by ship, and Kenzie has lost her mech. Book 5 opens with Zac ascending the fourth floor.

F-grade, peak, both bodies at level 75: Hatchetman and Undying Bulwark. Nearly 3 billion Nexus Coins by Book 4 Ch 93.