[[caption-width-right:350:We know the anti-sprial is terrifying, but damn...]]
For such an [[AwesomeMoments awesome,]] [[FunnyMoments funny,]] and [[HeartwarmingMoments heartwarming]] show, ''Tengen Toppa Gurren Lagann'' has some scenes that are [[NightmareFuel pretty darn scary.]]

Spoilers below... beware!

* The battle against multi-faced arm-sprouting huge Anti-Spiral ships. The opening mouths and eyes when the true strategy comes to surface (quite literally) will haunt viewers until the GrandFinale
* The first Gunmen that appears is pretty creepy-looking, not to mention huge.
* Kamina's scream after he is horribly mutilated by Thymilph's spear in episode 8 is bone-chilling.
* [[DeathByIrony Still...]] [[ImpaledWithExtremePrejudice Spinning...]]
* The results of Simon's HeroicBSOD following Kamina's death. Seeing the cute boy turn into TheBerserker who vanquishes {{Mooks}} with a NoHoldsBarredBeatdown, and is channeling so much UnstoppableRage that his mech actually [[DoesThisRemindYouOfAnything pukes]] [[DrowningMySorrows and shuts down]] is... rather unsettling, to say the least.
* Although it mainly doubles as a TearJerker, Rossiu attempting to commit suicide... is something.
* Watching the Anti-Spiral disassemble Nia is terrifying. Her body is literally being pulled apart digital bit by bit, and she's ''disappearing'' as it happens.
** It's even worse in ''[[TheMovie Lagann-Hen]]''. First, he ''disintegrates her bodysuit'' and then moves in on her with tentacles. Nia visibly struggles, and it's staged almost to make it look like he [[RapeAsDrama penetrated]] her.
* The Anti-Spirals. A HiveMind with [[SufficientlyAdvancedAlien god-like powers]] that has committed [[OmnicidalManiac the near-omnicide of Spirals]], their rap sheet includes: ripping off [[VideoGame/TheLegendOfZeldaMajorasMask Majora's]] [[ColonyDrop moon trick]]; having digital drones that can ZergRush you: inserting [[ManchurianAgent Messengers]] within every Spiral Race that [[ParanoiaFuel don't even know of their true nature until the time is right and could be ANYONE, even one of your loved ones]]; being able to trap their enemies in alternate realities that can be their greatest dream or (presumable, even though it never happened in the series) their worst nightmare; and they have an avatar who looks like [[Franchise/TheSlenderManMythos Slendy]] that has naughty tentacles and isn't afraid to use them. Oh, and the scariest thing about them? [[WellIntentionedExtremist They think they're doing the right thing]], [[KnightTemplar even as they cross the]] MoralEventHorizon over and over and over again. The only thing that prevents them from being one of the most depraved people in all of fiction is that they are truly convinced that they're the good guys; even then, that may not be enough to redeem them. Why? Because instead of just taking the easy way out and using their god tier powers to KillEmAll in one blow, they prefer to defeat their enemies by sending them over the DespairEventHorizon - and they [[EvilFeelsGood enjoy it]].
* The [[LotusEaterMachine Extradimensional Labyrinth]] as a whole. Being trapped in an infinite series of parallel universes until your body and/or mind dies? Combine that with the fact that you're ''completely unaware that you're dreaming''. That's valid cause for paranoia.
* The details of Lordgenome's reign becomes heavy Nightmare Fuel when examined more closely. He was once a noble spiral immortal warrior leading humanity against the Anti-Spiral threat, [[EndOfTheWorldAsWeKnowIt was presented with the worst case result scenario of his efforts]], and was convinced to slaughter his own forces, literally tearing them apart and blowing his own men and women to smithereens before forcing the rest of his own species to live underground as seen in the Parallel Works 8 OVA. He then has been spending the next hundreds of years sending his Beastmen armies to kill any humans who stumble to the surface. Additionally, he did all of this in a MortonsFork justifiable attempt to preserve humanity as a species, since a planetary destruction device that impersonated the moon was placed by the Anti-Spirals to destroy the planet if the human population ever reached 1 million.
** However, during his time as the Spiral King and ruler of the world, Lordgenome has been biding his time with sex slaves consisting of young girls kidnapped from various human settlements and brainwashed by his former battle ally Guame in a village under his control to be trained as sex slaves. He also impregnates and has children with the brainwashed girls, whom he raises and leaves to die in pods thrown into a far off canyon when they become too self-aware and question their existence. As seen in the anime, he has done this multiple times, as the canyon Simon finds Nia in is filled with other "failed Nias" who died inside their pods. Worst of all, none of this was necessary to his plan to preserve humanity. [[ItAmusedMe He did all of this because he was bored.]]