[[quoteright:297:https://static.tvtropes.org/pmwiki/pub/images/gantz-2347823_190.jpg]]
[[caption-width-right:297: And things are just going to keep on getting worse for Nishi...]]


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* Sure, the whole story can be seen as this, but shit '''really''' hits the fan in the Osaka arc. From the outbreak of the demons to the sick freaks that make up the Osaka team, it's hard not to be afraid.
* The Italy arc -- The fact that hundreds of Gantz teams are getting killed from the demonic statue aliens really dials up the nightmarish scenarios seen in this arc.
%%* The Dinosaur arc is no slouch in this department either.
* Which leads to how the Dinosaur Arc kicked off in the first place. Shion Izumi and starts shooting up the crowd in Chapter 123. All just to return to the game. Definitely a TraumaButton for those who suffered from urban violence.
* Apart from facing "fairly normal" horrific monsters time to time, there is the [[spoiler:Nurahiyon boss, Nightmare incarnate that starts as an old man that becomes an utter monster in the battlefield]]. Also, don't forget [[spoiler: the upcoming apocalypse... in a week]]. The apocalypse does not disappoint in this department (see below).
* The king of all nightmarish arcs, though, is the Catastrophe arc. As if the humans weren't in a bad enough shape already...
** And just when you think [[FromBadToWorse it couldn't get any worse,]] '''IT DOES.''' [[spoiler: The virus affecting Gantz causes him to create pixelated monsters that explode when they die.]] Read chapter 342 at your own risk.
** Chapter 347 is nothing but pure NightmareFuel. If a light spore touches a person, body parts and faces will literally burst from the said person's head and become '''AN ABOMINATION.''' Yeesh...
** One of the most horrifying elements is what the giants do with the humans they capture, with atrocities ranging from recreationally hunting them ''with their kids'' and feeding human giblets to their pets, to processing them in a mass-slaughter factory and casually snacking on them '''live''' (which fittingly triggers and justifies Sakurai's transformation FromNobodyToNightmare).
** The giant aliens have a tool that can "upload" a human's visual data from someone's mind and use it to track the person in question. Already ParanoiaFuel on its own, it's described in a deadpan tone by the aliens as not government or police equipment, but a ''children's toy''. [[FridgeHorror Let that sink in for a moment.]]
* The brief shot in the anime TitleSequence of Kei[[note]]who became a Gantz "team member" after [[DrivenToSuicide committing suicide]][[/note]] holding a Gantz gun to her own head. ''[[DissonantSerenity While smiling]]''.
* The Oni Arc features a scene with a shapeshifting alien that enters the ear of a RedShirt while transformed into a fly, it then moves to inside his torso and turns into a ''elephant''.
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