Rust agrees to pull the armies back unharassed in exchange for Carl pleading with Formidable for Earth.
The terms Carl extracts from King Rust are simple and straightforward: Rust will order the armies to withdraw back toward their line, and the crawlers will not harass the retreat. Both sides then get their last few hours free to prepare messages for their passing rather than spend them killing each other. In return Carl agrees to send Princess Formidable a plea to stop on behalf of the people of Earth, since Rust believes his daughter has always had a soft heart for the seeds. Rust concedes nothing about what happens afterward — if she backs off, he cannot stop what comes next in the dungeon, only guarantee the safety of the surface.
Rust says nothing once the negotiation ends. He simply turns and walks away. Carl instructs Princess Donut to keep pretending they believe in the doomsday, because the truce is worth more as a trap: once the horde disperses, he intends to strike them from behind, and wants Florin to have it ready. The deal survives only minutes — Rosetta beheads Rust before any withdrawal order can take effect, and the enemy charges instead.
The short-lived ceasefire Carl negotiates and secretly intends to exploit as an ambush.