Title: Brittle Bullet
Original air date: August 9, 2003

Summary:
Haruko begins to switch her attentions from Kamon to Naota, arousing the former's jealousy. They resolve to "duel" for Haruko, which amounts to little more than an intense airsoft firefight with Canti allied with Kamon. During the fight, Lieutenant Kitsurubami tries to unsuccessfully blow Canti away. Mamimi, observing Naota's intimate relationship with Haruko, questions him as to how much he really likes her, leading him to confront her about their relationship. Finally, his N.O. channel erupts with one of the largest objects yet, a leviathan robot, while a gunfight rages between Commander Amarao, his group of backup gunmen, and Haruko. Trapped on top of the robot, Naota resolves to save Mamimi and bravely fuses with Canti. However, despite his and Haruko's best efforts, they are unable to stop the giant robot, which rampages towards the Medical Meccanica plant. Canti then manifests the power of Atomsk by producing his EB-0 1961 Gibson bass guitar, to the amazement of Commander Amarao and Haruko. Canti defeats the giant robot, which is actually a gargantuan hand, rocketing over the Medical Meccanica plant and straight into the ground, where it becomes a petrified monument, presiding over the plant.
http://en.wikipedia.org/wiki/List_of_FLCL_episodes