This is My Final Duty

While the battle rages outside, Leeron steals a quiet moment with a gyroscope, musing about what lies past the heaven they aim for. A shockwave from Simon and Viral wipes out over half the smaller Mugann, but a massive beam from the lunar surface forces the Gurren Lagann to shield the Arc-Gurren behind a giant drill. Kittan's group takes over escort duty so the flagship's defenders can hold while the Gurren Lagann handles the moon, and the sight of friends turning the tide rekindles hope inside the ship, hope that feeds spiral power back into the shields. Simon proposes, rather than orders, that he and Viral wreck the cannon before a second shot, and the pair fling the mech's winged pack as twin boomerangs to destroy it. More cannons rise and fire in unison, so Simon catches the converging beams on an extended drill and hurls the energy back, scouring the surface clean.

The two giant Mugann then dissolve into component swarms that cage the ship and the mech alike. As energy pounds the Arc-Gurren, Simon urges Rossiu to remember every hopeless spot they have already survived, and Leeron realizes the vessel shares its design with Teppelin, another colossal Gunman. Powering free of the swarm, Simon and Viral drag the Gurren Lagann to the ship and sink the Giga-Drill into it, flooding the hull with spiral power until the vessel reshapes into the Arc-Gurren-Lagann. What survives of the enemy fuses into one titan, which the Burst Spinning Punch sends smashing through what Leeron suspects is a tear in space-time, wondering aloud whether spiral power itself is awakening.

The moon keeps falling. A vast face emerges across it, and the surge of spiral power rouses Lordgenome's head, which names the falling body as his own flagship. Schematics reach Simon revealing a slot where his power's wellspring can be inserted to take command of the vessel, the Cathedral Terra. Handing Gimmy and Darry the Arc-Gurren-Lagann's controls, he dives inside; Rossiu quietly resolves to detach the ship one minute before atmospheric entry, calling the survival of its 180,000 passengers his last responsibility.

At the core, Nia blocks the keyhole. Lordgenome warns that her body is built from the same substance as a Mugann, so destroying her would obliterate the control system too. She preaches terror and despair as the Anti-Spiral answer to spiral stubbornness, but Simon counters that hardship has only ever made his people stronger, and the engagement ring she never removed betrays her: he realizes she keeps appearing before him because part of her wants to be saved. Recalling how she once vowed to head toward tomorrow, he shouts for her to move and drives the Giga-Drill home. The descent stops, and the moon unfolds into a ship that dwarfs even the Arc-Gurren-Lagann.

Inside, Nia warns that neutralizing the eradication system means the Anti-Spirals now wage open war, and that the odds of her returning to herself sit near zero. Simon answers that anything above exactly zero counts as one hundred percent to him. Her old self surfaces long enough to ask whether he will really come for her, and then the Anti-Spiral homeworld recalls her, fading her away as he screams her name. Aboard the returning vessel, Rossiu concedes that Simon has once again turned everything on its head, and the Arc-Gurren-Lagann glides into Kamina City at sunrise.

The Arc-Gurren-Lagann debuts when the Gurren Lagann combines with the Arc-Gurren, and the moon is revealed as Lordgenome's flagship Cathedral Terra, the future Super Galaxy Dai-Gurren.

Simon shuts down the humanity eradication system, pushing the Anti-Spirals into a declared state of war, and Nia is recalled to their homeworld after confirming some part of her original self survives.

The Japanese title, Sore ga Boku no Saigo no Gimu da, corresponds to the English broadcast title This Is My Final Duty, a line referring to Rossiu's resolve to protect the evacuees aboard the ship. Japan saw the episode on August 26, 2007; the English airing came on October 27, 2008.

The episode sits between Episode 21 and Episode 23 and closes the Mugann conflict, pivoting the series from planetary defense to interstellar war.