In each episode of the FLCL series, a new robot appears and causes trouble for Naota and the people of Mabase. Created by Medical Mechanica, they come out through the N.O. channel in Naota's head. These robots come in all shapes and sizes, but they all have the same mission; to capture Atomsk and activate the Medical Mechanica plant.
This robot appears in Episode 1: "Fooly Cooly" was actually the left arm of a larger robot. It came through the portal in Naota's head at the same time as Canti did. It tried to pull Canti back through the portal, but Canti (who was fused with Atomsk at the time) broke the arm from its owner's body. The arm was still functional and acted as if it has a mind of its own. It moved by using its fingers to crawl and jump, and tried to beat Canti by crushing him in its grip. Canti was fused with Atomsk, though, and the arm was quickly outmatched. It tried to escape but Canti caught it by its loose cables and tore it apart.
This robot appears in Episode 2:"Fire Starter". It was the owner of the arm Canti destroyed in the previous episode. Its missing arm was replaced with a small but powerful tazer. At the beginning of the fight, Canti did not have Atomsk's power and was not strong enough to defend himself. The enemy robot was a very strong opponent and was able to detach and shoot its remaining arm over long distances. Haruko was able to land one good hit on the robot's left shoulder with her guitar, but for most of the battle she was busy dodging its projectile arm and was shocked by its tazer. While she was down, the robot went after Canti again. Just when all seemed lost, Canti "ate" Naota and regained Atomsk's power, and made an impressive comeback. Canti also transformed into cannon mode for the first time and blasted the enemy robot's single arm. Haruko then delivered the finishing blow and the robot exploded.
This robot appears in Episode 3:"Marquis de Carabas". It is unique in that it came through an N.O. channel in Eri Ninamori's head instead of Naota's. Staying attached to the girl, it took control of her body and used her legs for both attacking and defending. In the novel, Naota compares its appearance to a lemon squeezer. The robot attacked Naota first, but it soon went after Canti instead. After breaking a ukulele against it in a futile attack, Haruko came up with a battle plan. Luring the robot to the roof of the school, Haruko attacked it from above with her guitar while Canti attacked from below. The robot was undone when it happened to consume the super spicy curry from Naota's lunch. It dropped Ninamori and fell off the roof, allowing Red Canti to finish it off with a cannon blast.
This robot appears in Episode 4:"Full Swing". It was actually a satellite named "Shiosaki" and it contained a very powerful bomb. The satellite was knocked from its orbit by a baseball that Haruko hit into the sky and Naota's head was the beacon that guided it to fall toward Mabase. When it entered the atmosphere, the satellite's main body broke off from and kept falling toward Naota's position on top of the Medical Mechanica plant. Naota was able to stop the bomb's fall with his newly acquired guitar and Haruko hit it back into space with hers.
This robot appears in Episode 5:"Brittle Bullet". It was by far the biggest and most destructive to come out of Naota's head. It wore a long coat-like garment that disguised its hand-shaped body. It was actually intended to activate the Medical Mechanica plant. Upon exiting the N.O. channel it began walking through the city toward the plant, crushing everything in its path as it went and dwarfing all the surrounding buildings. When Haruko attacked it the robot revealed that it was carrying several gigantic guns under its cloak and opened fire on her. Canti came to Haruko's aid, changed into cannon mode and fired, but the robot knocked the cannon ball (really Naota) out of the sky and into a billboard. With no ammunition left, Haruko had only her guitar to fight with but it wasn't enough and she was shot out of the sky. The robot was finally defeated when Canti unleashed Atomsk's power and struck it down with a guitar of his own.
This robot appears in Episode 6:"FLCLimax". It was actually part of the one that was beaten in the previous battle. Called the Terminal Core, the Interstellar Immegration Bureau was aware of its existence and tried to find it before it could complete its mission. The small robot was lost in the river until the day Mamimi found it. Naming it "Ta-kun," Mamimi kept the robot as a pet and helped it grow by feeding it, first on cell phones and then on bikes. Eventually it grew too big for her to control and went on a hungry rampage through the city. Commander Amarao and Kitsurubami attempted to stop it but their guns were useless. After finding and swallowing Canti, the robot headed for the Medical Mechanica plant and attempted to fuse with the hand but it was still missing Atomsk's power. Haruko solved this problem by feeding it Naota--Atomsk's host. The robot then fused with and activated the hand, but it was stopped when Naota broke free, having fused with Atomsk himself. When Atomsk later emerged from Naota's head, he consumed the hand with his powerful N.O. channel.