- Everything about Cubia. Unkillable, seemingly unstoppable even compared to the Phases, and clearly something that just shouldn't exist. He isn't even a part of the Phases, as he's essentially Kite's / the Key of Twilight's anti-existence, meaning that not only is he a semi-natural part of The World, Aura likely very well knew he'd exist given that Helba figures out immediately what he is. Things only get worse in G.U., when he's reborn at the end of the series in an even more horrifying state as Haseo's anti-existence and the True Final Boss, with no foreshadowing up to that point.
- In the second cutscene of .Hack//OUTBREAK, Kite has a brief reunion with Mia, who has been with him for the last two volumes. However, she acts strange, has obscure dialogue ("we can go back and forth freely now," implying that she is going to become one of the Phases entering the real world and wreaking havoc) and makes gestures that imply that all is not well upstairs. And when Kite goes to touch her, she screams at him. Couple this with the accuracy of her English VA, as well as the extremely distorted textures of the current area and you have a scene that should not be watched with the lights out. Here's the scene, for those curious.
- Data Drain and the effects it has on normal player characters. We get to witness what happens to Orca up close and personal in .Hack//INFECTION as Skeith status-breaks him and then blasts him with a Data Drain; he legitimately screams in pain, and is added to a steadily growing list of players put in full-blown comas. No one even knows why they're happening besides trying to link it to The World, which is actively being covered up by the developer altogether. The fact that this returns with all the danger it entails in the G.U. series is not played down at all, either.
- Kite is in junior high school, presumably about fourteen-years-old if one goes by extra information released after the original R1 series; even Black Rose is older than him (something she points out in her e-mail chain). And he gets to witness his best friend in real-life effectively 'die' right before his very eyes on his first day in The World without knowing what is even going on or being able to prevent it. This isn't even getting into the sheer amount of hell and trauma the poor kid has to endure over the course of the rest of the series, championing a battle against virtual abominations that could put him in a coma if he ever slips up on a daily basis with the fate of the internet and eventually the world in the balance. The fact that, after everything is said and done, he seems to be fairly well-adjusted in a franchise filled to the brim with Dysfunction Junction speaks leagues of the kid's fortitude compared to Haseo's freakouts and the long time it took for him to get over his own problems.
- The Twilight Bracelet itself is no slouch in this department either. With each Data Drain it performs, Kite's character grows in data corruption. Should he ever overtax it, it will kill / make him comatose, and it's implied to be causing him physical pain in the real world - but he has no choice besides use it given that nothing else can do what it does. The fact that making it stronger also made Cubia stronger also means Kite is essentially feeding the most terrifying entity in the entire franchise.
- Skeith, followed by the rest of the Phases. To say that most fans won't forget their first real encounter with Skeith is an understatement, but everything gets worse from there.
- To start with, Skeith only appears a couple times in Part 1 but each time is significant. From his Curbstomp Battle on Orca (a legendary player who can't even damage Skeith but hits him once for a Data Drain), to his finally catching Aura at the end of the part and promptly Data Draining her before spliting her into three fragments, this entity never speaks a single word, is downright ruthless and efficient and only ever makes noises when attacking while never once even touching the ground or walking. When people think of non-human antagonists for the franchise, Skeith is easily one of the first. And his title that becomes more prominent in the G.U. series? The Terror of Death.
- The Phases are all as alien as can be. Skeith vaguely resembles a humanoid golem to a bare minimum, but the rest of the Phases are just plain freaky forms like walls, stained glass eyes and so forth, especially once Data Drained. Their mere introduction as a boss fight causes the entire game to part seas of static and corrupted data before they zoom straight up into your face and get a title card, unlike anything else in the game. And they're all devastatingly powerful, have Data Drain, and require to be Data Drained to be able to even hope to actually kill them.
- At the end of Part 1, you triumph over Skeith, and feel some sense of accomplishment seeing as it was far and above anything else you've fought in the game up to that point. And then Kite has a rock fall on his head. He stares up, and all he can do is stare in sheer horror at the titantic behemoth of the aforementioned Cubia, beating heart of a core visible inside and a gigantic multi-eyed skeleton face as tendrils and vines grow out of its sides. The game doesn't even give you a chance to fight it; a single blast from its mouth, which alone causes the game to distort and corrupt, knocks Kite clean out from an indirect shot.
- The sheer damage The World sustains over the course of the first generation games, and the corruption as a result. Corrupted areas have holes in the data that show the code beneath, Data Bugs can appear depending on the area or quest and become normal enemies in part 4, and there's always something off-putting about it all considering the circumstances. To top it off, corrupted areas occasionally hit you with a burst of static noise and the screen color inverting. You can even see large gaping holes in the skies of these areas, with nothing but eerie lines circling outside the cracks.
- And this isn't even the worst of it. Thought you were making progress throughout Part 2 in stopping the corruption? The ending reveals the corruption is spreading to the hub towns and across the game now, CC Corp can't stop it, and destroying the Phases makes The World more and more unstable. Thankfully this just has the visual side-effects, but that means for the rest of the series those areas will always feel uneasy as a consequence.
- However, while the corruption is more or less aesthetic in the game, it begins to outright screw with the real world; a scan of the news application in the Main Screen of the Operating System shows that The Phases and Cubia are gleefully doing targeted attacks on humanity like wrecking traffic lights, disabling power to large swathes of Tokyo (as seen in Liminality) and likely elsewhere, and even shutting the entire internet off for large spans of time. The implication is that the Phases are actively seeking to cause an Apocalypse How, possibly up to a Class 2.
- The Net Slums. A uniquely corrupted area in its own right that is some of the in-universe remnants of The World's unused data, it's a hodgepodge of modern geometry that doesn't quite fit the game combined with assets of the fantasy setting, abnormal denizens which include having TVs with emoticons for heads, and mismatched textures resulting in realistic human eyes on walls, or pixelated symbols in the middle of the normal ground. The somewhat-ambient music doesn't help at all, either. And the kicker to all of this? It's a hub town area you'll come back to numerous times and these problems never go away or get better. Although to some that might be Nightmare Retardant instead.
- Haseo, at least towards the latter half of ROOTS and the beginning of Rebirth post-timeskip. He went from a fairly regular player to a Player Killer Killer who looks like the devil as he mercilessly slaughters Player Killers. The establishing cutscene for this even has him use his broadsword's chainsaw blade to saw a player down without batting an eye. And even post-Data Drain reset, he hinges back into this upon gaining Skeith as his Avatar. G.U. Trilogy only amplifies it up with Glowing Eyes of Doom and more twisted expressions and sheer rage.
- Reminisce starts with one of the most extreme examples. The entire active playerbase being trapped in the game just as Tsukasa was. When sent to check on the other players, some will make mention of their friends not coming back after being killed. The first Area Haseo visits is full of Kestral players who have come to the conclusion that they need to kill everyone they can to be able to escape the game. Though the situation is resolved in what seemed to be just hours, the time that had passed in reality was mere moments. This leaves the players that witnessed this and attempted to call CC Corp out on it being labeled as trolls or people with overactive imaginations at best or insane at worst, all the while CC Corp is, as usual, doing everything they can to cover it up.
- The CC Corp, named after the developers Cyber Connect 2 that made the .hack franchise in the first place. At first they seem like Incompetence, Inc., what with how they constantly try to cover up the glitches and abnormalities, and even ban players that dig too deeply while being fishy as hell the entire time. Then the end of the original series comes around, and afterwards they experimented on the Epitaph and nearly caused Cubia to revive, which is what caused one employee to go and burn down the R:1 servers so the idiots didn't end the goddamn world again. They're so wildly inept at anything other than trying to cover their own asses and silence the truth, that by the time of G.U. as things escalate yet again, they almost veer straight into an apathetic routine of demonstrating just how little they care about anything other than their profit margin while the lives of their players constantly dangle in the jaws of danger. In almost every other series or installment.
- How stupid are they? When a crazed Sakaki threatens to cause more coma incidents and wreak havoc on the players of The World by way of blackmailing CC Corp, they silently give him control of the game while trying to yet again save face in public and act like nothing's happening.
- Granted, a lot of the real serious problems happened due to Harald's desperate postmortem attempts to cause the birth of sentient AI with a massive lack of hindsight about the idea, but it says something that despite having a high level admin working with the .hackers and knowing just how deep the rabbit hole goes, their inclination during the final battle with Morganna in the original series is to try to shut down the servers and hope the problem goes away. Which would either render all the comatose victims unable to be saved, or potentially even outright kill them, while having a high probability of failing to contain the threat.
- It gets worse; in the Beyond the World story, Virus Bugs appear yet again and put more people into comas. Why? Because CC Corp created them this time around to attempt to force people to buy their anti-virus software, except they Grew Beyond Their Programming and started wreaking havoc on society. Simple corporate greed ended up threatening a social collapse not unlike Morganna and the Phases, and the only people with remotely any proof of this was a federal agency that had no capability of acting on it themselves. It's hard to tell if they're even Stupid Evil or just that apathetic in the hunt for profit.
- Speaking of Beyond the World, the entire concept of the Eco-Terrorist group, "mama". To wit, they're not only infiltrating governments and organizations in an attempt to create a digital utopia for humanity so that Earth is left alone, but they're totally willing to gun down and kill people who get in their way if they can get away with it. They were also the founders of ALTIMIT, meaning that the monopolization of a single operating system in a post-Pluto's Kiss internet really was a conspiracy. They are singlehandedly the highest escalation of a threat level in the franchise, and entirely human at that.
- If that weren't bad enough, (MAJOR SPOILERS) the woman named Emma that Harald tried to create Aura for as their sort of 'daughter'? She was a leading member of "mama" who Harald fell in love with, but was just personally exploiting the man's programming talents to her own ends. The Epitaph of Twilight? Essentially a blueprint for Harald to emulate, meaning all of The World R:1's problems were plotted out by a wealthy eco-terrorist with too much influential power, even if she couldn't have foretold how they would play out. And by all means, she technically succeeded in her plans to cause the birth of Aura. Emma Wielant was, in essence, a Greater-Scope Villain for the entire franchise, and to top it off she may have even faked her own death and gotten away with all of it.
Nightmare Fuel / .hack