* AngstWhatAngst: A lot of the times, the characters will get a little upset but move on rather quickly from the tragic, stressful events around them like [[spoiler: discovering that your first love got gang raped to death, finding out your best friend turned into a mass murderer or Zaji dying.]] Justified in how the characters are constantly in danger and can't afford to dwell too much on the negative things.
* CompleteMonster: [[BigBad Takashi Nishikiori]] is a [[TheSociopath sociopath]] with a [[{{Sadist}} sadistic love for tormenting and torturing others]]. Once crash-landing on an island with hundreds of other passengers, Nishikiori [[ManipulativeBastard establishes himself a power base]] by blackmailing a large group of people into serving him in exchange for him giving them the antidote to a lethal plague they have contracted, claiming to be a doctor. When the group's leader tries to swear allegiance to save his young daughter's life, Nishikiori refuses to cure the duo to ensure no threats to his power, laughing over them as they die in agony. As leader of his group, Nishikiori encourages whistleblowing and betrayal amongst his followers, brutally beating and torturing any who try to stand against him, all while [[BadBoss having zero problems sacrificing the lives of those loyal to him]]. When confronted by [[TheHero Akira Sengoku]]'s group of teenagers, Nishikiori tortures them, sends them on a suicide mission, then attempts to [[ManOnFire burn]] the dozens of [[WouldHurtAChild teens]] alive one by one, forcing the others to watch and cackling at their misery. In his worst scheme, Nishikiori captures all the females in Akira's group, then forces the males to try to rescue the girls, planning to execute one girl for every failed rescue attempt. Nishikiori then tries to force the girls themselves to sentence one of their own to die, secretly promising his men the chance to gang-rape all of the girls left alive once their "game" is done. Even when beaten, Nishikiori takes sick glee in revealing he's not even a real doctor who can cure a dying student's ailment, and makes one last attempt at screwing everyone over by taking a little girl hostage to make his getaway and leave everyone else to die. Nishikiori's presence on an island filled with monsters and mutations solidified the idea that sometimes, [[HumansAreTheRealMonsters man is far crueler than any beast]].
* EndingAversion: The manga was extremely popular during its run until its [[CutShort abrupt]] LeftHanging ending, and it was likened to Series/{{Lost}} in both a literal sense and in unfavorable terms, at which point some were advised to nto even bother starting and getting attached to the series.
* EpilepticTrees: Everything in the series.
* FanonDiscontinuity: Many fans preferred to pretend the ending doesn't exist and treat the plot as a straightforward survival drama.
* FanPreferredCouple: Akira/Mami started rapidly gaining popularity even though [[OfficialCouple Akira/Rion]] remained the flagship pairing regarding a protagonist who may as well have had a harem.
* FetishRetardant: How some feel about the fanservice. PantyShot and ClothingDamage? Hot. On girls who are dead/dying/in serious danger? Creepy. This combined with the occasionally misogynistic atmosphere can make the manga a kind of uncomfortable read.
* HoYay:
** Kouhei ''really'' wants to find Akira. [[spoiler:He also states that while he can't bear to show himself in front of Akira anymore, he will protect him from the shadows.]]
** Yarai and Akira have a bit of this, too. In Chapter 141, Yarai actually [[spoiler:''cries'' because he doesn't want to kill Akira, but Nishikiori won't save Kurusu-sensei if he doesn't.]]
* MoralEventHorizon:
** [[spoiler:Kouhei]], up to then one of the nicer characters, kills a girl on the mere suspicion that she saw him stab the pilot.
** [[spoiler:Nishikiori]] jumps over the line with every appearance. It really says something when the nicest thing he's done is send a bunch of kids on a suicide mission.
* {{Narm}}: It is difficult take seriously a dramatic situation while the girls show their panties at readers.
* NightmareFuel: Being stuck on an uninhabited, mysterious island with [[EverythingTryingToKillYou every large and dangerous prehistoric species out to eat or maim you]] is ''not'' a Happy Fun Time. So you can bet that the series is full of this.
** That's not even counting all the humans on the island either. One of the main themes of the manga is that wild beasts aren't the only animals to be scared of.
** [[http://www.mangahere.com/manga/cage_of_eden/v17/c143/19.html This]] [[EldritchAbomination creature]] qualifies
*** [[http://www.mangahere.com/manga/cage_of_eden/v17/c150/13.html This]] looks more like a demon than an extinct animal
** [[spoiler:Nishikiori]]'s brainwashed slaves, who keep serving him despite all logic and reason.
* TheScrappy: Suzuki spends of his time being an arrogant, manipulative pervert. It goes to the point where fans were actually ''happy'' when he was attacked by the bird. Several fans were disappointed in chapter 93 when he was attacked by ANOTHER species of bird, but was then spat out.
* {{Squick}}: In general, the manga doesn't pull any punches in showing ''exactly'' what teeth[[note]]or beaks, or claws, or [[EverythingTryingToKillYou everything else]][[/note]] bigger than your head can do to you...
** Or big falls.
* TooCoolToLive: [[spoiler:Zaji]]
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