This article contains information that relates to the non-canon game Pikmin: Ultimate Doom by Wraith.
Rust Factory is the sixth area in Pikmin: Ultimate Doom. It is themed like a huge, rusty metallic factory with lava flowing underneath. Rust Factory is the third area that is underground, in which it's located inside of a semi-active volcano. There are many rocky surfaces and rusty iron surfaces. Red Pikmin come in handy here, as many fire traps are set off on this level. Also, Red Pikmin are resistant to lava, so they can cross a stream of lava and hit the switch to stop it on the other side. Many rock-like creatures emerge from the lava, and two Spotty Bulbears patrol thier own halves of the level, pursuing and killing the player's Pikmin. No Pikmin are obtainable from here, but certain items are.
Louie's helmet, evermore cracked, leaks a small amount of steam when he first steps out of the Trailblazer inside Rust Factory. You may notice he is slower and throws Pikmin slightly slower, and needs to take breaks every third of the day. Olimar and Pikmin march on, exploring the deep economic escapades of the ancient Pikmin Planet civilization. After notetaking, Olimar notices that many devices and machines nearly fit his and the Pikmin's hands perfectly. He assumes the civilization is bipedal and very similar to Pikmin, but larger. He wonders what happened...
Upon Area Completion
Olimar, expecting some kind of sign to the next area of expedition, is disappointed when nothing significant happens. He supposes he should finish exploring the previous areas and scooping up the rest of the treasure.
Upon All Pikmin Planet Completion
Olimar and Louie are summoned to Rust Factory by a strange voice. They dismount the Trailblazer, retrieving the Pikmin. Then Louie sees the shadow of a massive creature. He shivers as the ground tremors, cracking his helmet open. Gasping for his air, a temporary bubble shield is activated. The clock starts with a timer of 10 minutes until life support fails. As per Hocotate Franchise's policy, the company property self incinerates itself after the host has died, meaning Olimar and the Pikmin would all perish in the blast. The boss roars and Olimar recognizes the creature as Penumbra, but beefier and with darker features. It emits a black aura of hatred, and Olimar names this new form Ultima Penumbra.
After the boss is felled, he collapses into a singularity. The black hole sucks all the Pikmin in, along with Olimar and Louie. The Trailblazer, gimping away, falls into the dimensional pit as well. They do not believe they will survive, but time makes them, as they begin to see the light of day again after what it felt like as hundreds of days in twilight.