In How I Became Yours, as Azula is regaining her lightning bending powers, Mai takes the opportunity to throw a knife into her chest, which nearly kills her. This averts Talking Is a Free Action and shows that mundane weapons, even ones as seemingly unimpressive as knives, are a threat against benders.
Aang's sparing of Ozai put Zuko's legitimacy as Fire Lord into question and loses him the respect of his comrades, seeing they all told him to kill Ozai and he put his beliefs over the good of the world.
When Zuko is hit by lighting, he had to see a real doctor and was comatose for a few days and bedridden for a week afterwards.
In the prequel Jet's Troubling Obsession, when Zuko tries to show Jin the view of Ba Sing Se, she lacks the fitness and strength that most of the Avatar cast has and had to be assisted by Zuko to get on the roof; this was supposed to compare the cast to normal people.
In a fic actually called Reality Ensues, Unohana learns the hard way that she doesn't get to just die peacefully in a Heroic Sacrifice, especially since the Bleach universe has so many ways to cheat death and nobody with half a brain would let her stay dead since they need her to help against the Vandenreich.
The Joker seemed satisfied, "NOW!" he clapped his hands together. "Where's ole little Griphook?" The tiny goblin stepped forward reluctantly, not pleased at all that "Harry" had remembered him.
When Harry Potter winds up in the Star Wars universe in Havoc Side of the Force, he doesn't understand a word of (almost) any language used and becomes a smuggler to support himself as he has no knowledge, money, or identification that could help him.
During the Halloween spell in The Hell-er-Nator: Chaos Machine, things are far more serious than canon. The titular Terminator, pirates, and others cause easily dozens of murders, rapes, and arsons. Children are forced to become soldiers or die horribly. And while the police are doing what they can, there's so much chaos, a detective remarks that soon they'll be down to half a car and a dog for each crisis (then notes that they don't even have enough manpower for that).
In Here be Dragons the protagonist's mostly civilian crew tries to play Big Damn Heroes against an enemy powerful enough to capture two Jedi... and swiftly get their arses kicked, needing The Cavalry to save them in turn.
Mare Genius: Pinkie tries to surprise combat-trained Agatha with a Party Cannon and gets exactly the kind of counterattacking Reflexive Response you would expect from someone seeing what appears to be a weapon pointed at them.
Singularity doesn't just make people float around haplessly. Here, victims get sucked in and turned into Ludicrous Gibs.
Chapter 36. No matter how strong your Healing Factor you will still go down after getting hit in the head enough times.
Chapter 41. Wreav may be Bio Augmented up the wazoo but he still will fall when multiple squads and a Wanzer empty their weapons into him.
Also from that chapter, infantry-scale attacks, even from the second strongest known human biotic, aren't going to do anything to a building rated against nuclear strikes.
Subverted in Mikami Vs. the Cybermen. After eight days straight of writing, he mentions how surprised he is that he hasn't run out of ink. Double Subverted right afterwards, when he dies of thirst.
Played with, though also straight, in the 1983: Doomsday Stories, which has Austria hoping against hope that Hungary survived Doomsday. She doesn't. Though it doesn't stop her from looking after him even after death.
No Chance For Fate is built on this trope. Reality ensues hard on the common tropes of the Fuku Fic as well as on the source material of both series. Too many to list here. However, despite or maybe because of this, the story reads well.
In A Spark of Genius, Leviathan aka Xander uses his portal technology to blast Hawkgirl with arctic water. Xander's banter is cut short when he realizes she's entering the first stages of hypothermia and he quickly teleports her to the Watch Tower's med-bay.
When Tony Stark stops all production of weapons by his company and switches to electronic devices (such as computers and phones) in A Third Path to the Future, thousands of employees are laid off (and hired by competitors) as their skills aren't compatible. Though Emma Frost does note that while Stark's former employees do resent him, it's far less than expected.
In White Devil of the Moon, Nanoha realizes that Princess Serenity could have caused a diplomatic incident if she came to harm in any of her trips to Earth, and when she fell in love with Endymion, he might have turned out to have been an unscrupulous individual seeking the throne.
Pepper Potts is not impressed by Grey's attempts to stalk her or mail her a BDSM contract without her consent. She ends up appealing to Black Widow and Hawkeye for protection, to put an end to the stalking.
When She-Hulk is told about Christian trying to rope Pepper into said contract, the first thing she says is that such contracts aren't legally binding. When Christian mails her a copy of Tess of the d'Ubervilles and compares him to Alec and her to Tess, she notes that Alec was a horrible person and using him and Tess as a literary couple is not a good way to compare a real life relationship. When she wakes up in a hotel room after getting drunk and finds that Christian removed her clothes and won't tell her where they are, she freaks out and runs out of the hotel, telling Black Widow (who was searching for her outside) "Thank God. I think my client is a creeper."
Jane is appalled instead of turned on, when Christian tries to finger her at his family's charity event.
On the flipside, while She-Hulk thinks that Christian is a sleezebag and very much supports Pepper filing charges against him, she still takes his case against Hawkeye and Black Widow because them attacking him in defense of Pepper, while understandable, was still illegal. This is followed by She-Hulk having to drop the case because Christian starts trying to force her into a romantic relationship with her, which makes business arrangements between then unethical.
In the Teen Titans fic Consequence of Misunderstandings, Starfire attacks Raven (who left the team five years prior) while the latter is on a date. Afterwards, not only does the Titans' reputation take a major blow, but the entire situation becomes an interstellar incident since Starfire is Empress of Tamaran. Batman lectures them after hearing "all the details about that debacle from various media sources. And from the Department of Justice. And the State Department, the Department of Defense, Homeland Security, and the leaders of the Armed Forces." Furthermore, the fact Starfire ordered three battlecruisers into Sol's heliosphere without informing the Justice League or the Armed Forces is treated as an act of war. She's given twenty-four hours to get them out of the system or they'll be destroyed and she'll be deported from the planet and barred from ever returning.
Light imagined that when he'd moved in with Ryuk in the Shinigami Realm that he would make a clean break with his old life but soon discovers that making the Shinigami realm habitable is actually a lot of work and he has to make frequent trips back to the human world for groceries and supplies.
Also lampshaded when Light decides that he and L are Better As Frenemies seeing as a mutual desire to see each other dead is not a good foundation for a lasting and loving relationship.
The police sue L for the illegal and unethical way in which he handled the Kira case—namely his stalking and harassment of a teenage boy.
In Fever Dreams L and Light get sick from staying out in the rain for an extended period of time.
Yamamoto: Kira or no Kira crime is never going to disappear. People have always been afraid of dying. That hasn't stopped them before—it's not going to stop them now. Criminals are just gonna get smarter about it, that's all.
Yamamoto: If you think about it, there's plenty of ways to exploit the Kira situation. What if you want to get rid of your enemies fast? Just frame them for murder and get their name and photo on the six o'clock news...
As demonstrated in Spira Mirabilis Light's desk trap involving an electric current that would ignite a plastic bag of gasoline is not a good idea and the way he has it set up it would blow up even quicker in real life. (By quicker we mean immediately. Gasoline melts plastic).
A Story of Stupid shows what would happen if someone recognized Light while he was out manipulating Naomi Misora. Also Sayu overheard her brother shouting at the television:
Sayu: Why is he screaming to the TV about justice? […] Wow. My brother's on crack.
River faces off against a rival pirate crew's Arrogant Kung-Fu Guy. The battle begins with them sizing each other up, and with the martial artist declaring River as a Worthy Opponent, who might be able to truly test his skills, and he rushes at her with his bo staff. River shoots him twice in the head. Then she demands chocolate.
Later on, River is facing a group of vengeful pirates. She's on the ground, and they're in their ship. She starts running for cover behind some boulders where they can't shoot her, only to get hit by the backwash of their engines and get thrown into said boulders, breaking her legs and back.
Hans and Heins have a harder time pretending to be a profession than most fictional characters. When pretending to be ice harvesters, they end up making some amateur mistakes, one of which results in an accident that almost gets Heins killed and is decidedly not Played for Laughs.
Boys Und Sensha-do, found here has "simunitions" for the tanks in tankery, as the author believes tankery is otherwise dangerous enough. Despite this, Miho ends up being seriously hurt when she accidentally gets hit in the chest by a shell, and would have lost her legs if the tank had accidentally rolled over her.
The Boy Who Died shows the consequences of making little Harry Potter a famous figure, icon of the Light, and the enemy of dark wizards everywhere before he even knows how to talk let alone protect himself.
In Changes Dumbeldore's excuse of "I know what's best" doesn't cut it in a court of law and when his history of child neglect comes to light he is stripped from his position as a school headmaster.
When Amelia Bones finds one of her aurors (Tonks) sneaking into a restricted area on Dumbledore's orders, she fires Tonks on the spot. "Leader of the Light" or not, aurors aren't allowed to take orders from anyone outside the chain of command.
Harry learns that his Firebolt was destroyed beyond repair while being checked for curses and the professors covered it up by buying a new one with his money. It's noted by Susan and Amelia Bones that it'd take longer for the manufacturer to repair it or build a new one than the amount of time the teacher's allegedly took to fully strip it down, check it for curses, and rebuild it.
When most of the professors and several members of the Order of the Phoenix help Dumbledore drug the Hogwarts students with potions to make them accept anything they see or are told, along with imprisoning anyone who escapes their dosing, every professor who helped (and every Order member) is arrested on the spot. According to Madam Marchbanks, Hogwarts will be closed at least temporarily given that almost the entirety of it's staff is going to be fired.
If Thems The Rules shows regardless of Harry raising Tom Riddle in better circumstances and giving him an ideal childhood, Tom Riddle is still a sociopath.
In Lord of Caer Azkaban Harry sends in his elite team of soldiers to take out Voldemort and his Death Eaters. Harry doesn't participate in the battle himself because he knows that, as an untrained student, he'll just get in their way.
A Necessary Gift shows that even if you defeat the Big Bad that doesn't mean everything gets magically better or his followers (and the prejudiced ideology he espoused that allowed him to gain power in the first place) will go away. In fact things get worse because the only one who could control the psychos is no longer around...
As mentioned in an author's note in the AURaised By Darkness concerning why Sirius Black isn't immediately released from Azkaban; because although Minister Fudge has grown a backbone in this fic and "is being nice to Harry and the Dementors he has no evidence to suggest Sirius Black is innocent and he still wouldn't believe Harry who is close friends with the man."
In Wish Carefully it turns that the Light lost to them on purpose, and because they exiled all Light supporters and muggleborn they have no economy or people to lord over and Dark wizards tend to be the very bottom or very top of society. Their society is slowly dying off due to frequent inbreeding and social mores preventing large families.
You're on my side? shows what happens when leaving little Harry Potter with so-called guardians who hate him and don't care if he lives or dies.
In An Alternate Keitaro Urashima Keitaro refuses to run the Hinata Inn since, not only are several of the girls violent and don't want him there, he's got his own life to live and can't devote that kinda time to running the dorm. When Granny Hina tries to play the childhoodpromise card, Keitaro points out that you can hardly expect someone to stick by a promise they made when they were five. And finally, Naru's and Motoko's chronic violence comes back to bite them both. Naru is treated as a pariah after several students see her punch out Keitaro while he's talking to Mutsumi. And Motoko is arrested for assault with a deadly weapon when she attacks Keitaro with her katana.
Kaolla Su decides to "cheer up" the guests at an inn by chasing them with exploding Mecha-tamas. Dozens are injured, the inn is nearly destroyed, and Kaolla is arrested as a terrorist.
Naru's Hair-Trigger Temper gets her into some very hot water when she punches a man that she assumed was making creepy passes at a woman. The man and woman are revealed to be a married couple and on top of that, he's revealed to be the career adviser at Tokyo University Naru had an appointment with, meaning Naru essentially put her academic future and job prospects in jeopardy.
In Love Hina: Like It Could Have Been, when the girls angrily declare that they'd never let a man be their manager, Keitaro leaves, having compromised with his parents (and thus not being forced to live at the Hinata Sou). Later Kitsune is told to either pay her rent by the end of the month or find a new place to live, and both Motoko and Naru are smart enough to rein in their hatred of men so carpenters can fix the damage Su's inventions have caused.
In Oneesama, Shizuru giving a Skinship Grope to Natsuki is treated as sexual harassment by Miss Maria, who says Shizuru could be expelled if she felt it necessary. Thankfully, she's also a Reasonable Authority Figure, and decides on a punishment that forces Shizuru to humble herself and approach Natsuki as herself, rather than her persona as top Coral.
In Perfection Is Overrated, a handgun is significantly less powerful than most of the Himes' Elements or Childs, but it still has enough power to kill someone. Shizune, whose special ability made those of the Himes useless finds this out the hard way.
In Renegade ReinterpretationsHumans do NOT magically Advance Swiftly. As such, when the Batarians come visiting, they get Curb Stomped over and over again and only Zerg Rushing enables them to desperately throw lives for time in the hope of being able to turn the tide someday. After they do so, the cultural scars of the generations-long war means that mankind does not magically become receptive to further alien contact.
The Starvation Side story also explores what would happen if the barrier caused a massive displacement of people and a large part of the world being left unable to produce food. Simple foodstuffs have become luxuries pretty much, and people are willing to risk their lives fighting in the war to get food rations.
The Calm Before the Storm Side Story also illustrates the consequences of what would happen to a country if it had a sudden, and very enormous population boom. It turns out that TCB!Equestria is suffering from food shortages, rapid industrialization that is ruining the environment, and does not have enough space or the adequate infrastructure to to support all the newfoals that came in. Not to mention, a prolonged war with innumerable casualties is bound to completely destroy the fabric and the general morale of society, so much so, that in the end only terror and fanaticism can hold it together. And barely even that is enough.
The Equestrian Civil Service Series is all about this. In a realm of gods, monsters, heroes, epic adventures (and Royal Brats), there still needs to be somepony to run things behind the scenes, leaving the eternally Beleaguered Bureaucrats to deal with everything from imminent disaster to the fallout of a visiting celebrity to a castle covered in custard.
The Finger Trap has Twilight Sparkle appear on humanity-occupied earth, and go to the first house she can see to ask for directions. Instead of a person who sympathizes with her and wants to be friends, the main character is the one contacted... who distracts her long enough to call Animal Control.
In Self-Insert FicAberrationOccidental Otaku Rae trips into a portal and is transported in Konoha. Does she learn cool jutsu, gain a bloodline or take a level in badass? Nope. She is stuck homeless in a world alone with nothing but her clothes on her back, will never see her family and friends again and is unable to learn any jutsu because she's from another world and doesn't have chakra. While she does find her place in Konoha, she remains a normal civilian woman and can not compete with a ninja.
As Destiny Is A Hazy Thing shows, an invasion that severely weakens two of the five great villages when all villages are in a constant Cold War is liable to set off the next World War.
The Sasuke retrieval mission was a success, although Naruto lost his right arm (worry not, for it grew back). Sasuke, however, is charged with treason and locked up in ANBU prison with his ninja status (his chakra network is also shut down) revoked without any chance to regain it or any parole. Made worse due to attacking Naruto, a fellow Leaf nin, and placing the others on the mission in danger. Naruto himself doesn't dispute the punishment.
After years of dealing with Sakura (who'd commit Domestic Abuse on him at any time or call him an idiot or a perv), 13 year old Naruto has the notion that ALL women will beat him for anything even something out of his control leading to a rather OOC (read: quiet) Naruto on a trip with Tsunade, Shizune and Hinata and a case of accidental Covert Pervert. Tsunade sits him down and tells him "No. Sakura just had issues. We are not going to beat you for something as stupid that."
When Konohamaru attempts to attack Sarutobi in First Try, Naruto (who's currently suffering from PTSD) nearly kills him on instinct. The only thing saving him from getting a kunai through his skull was Sarutobi grabbing Naruto's wrist in time.
Offscreen Inertia is fully in play when Naruto and Hinata leave the village for training. They come back a week later and Konoha is in ruins courtesy of the Akatsuki.
Tsunade snaps at Jiraiya saying that since Naruto came back (from the 3 year training trip), he's been in fights with S-class nin after S-class nin. Jiraiya says it will make him stronger. Tsunade says he's more likely to die. Guess who was right.
In The Scorned Son, the Wave mission is a failure because teamwork or not, three ninja barely out of the academy don't really have a chance against a Jounin that's trying to kill them for real. The end result: Kakashi is dead and Kiba nearly kills himself keeping Sakura and Naruto alive long enough to find help.
Team 8, Naruto warns Lee not to pursue Sakura's affections because she is not a good person. Unlike other stories where Lee would have disregarded Naruto, he takes the latter seriously and laments that such a pretty girl is so mean.
In It's a Wonderfully Splendid Magnificent Life, while Tamaki is viewing his life if he'd never left France, what finally convinces him to keep things the way they are is seeing him and his mother living in poverty, with him struggling to pay her expenses. What really makes this a Reality Ensues moment is that being together as mother and son does not make up for this for either of them, in stark contrast to many works that would indicate that being together as a family is most important.
In Innocence, Misty confessed her feelings to Ash in the backstory. This nearly broke their relationship apart as Ash, being a ten-year old Chaste Hero, had no idea how to respond.
Cilan in Identity Crisis who along with his brothers, turn out to be a part of the Shadow Triad and The Mole is torn between the people he genuinely became friends with or his brothers and his organization. Does he pick a side and affirm his loyalty to them? Nope. His wavering loyalty cost him his relationships on both sides as his brothers no longer trust him as he's not truly committed to their cause and his friends are angry that he wasn't really their friend and initially intended to backstab them.
In Like No One Ever Was, one of Pikachu's Thunderbolts ends up getting Ash hospitalized and possibly permanently ending his trainer career with Ash suffering from major internal damage and brain injuries. Apparently even before that fateful Thunderbolt, Pikachu's friendly shocking of Ash has slowly deteriorated his muscles, meaning his journey would have been coming to an end anyways. Pikachu is horrified when he learns of this.
Poké Wars has several examples, including: being too close to a Magmar will cause you to burst into flame just from the superheated air, Elemental Powers are very destructive and lethal forces, multiple hotspots of 18,000F heat will cause terrible environmental damage, Olympus Mons fighting will result in severe and permanent environmental damage, and mass panics can be just as dangerous as the disaster itself.
In The Sun Soul, a(n insane) bug catcher pulls out a knife that was stabbed into his leg. Blood starts gushing out immediately, since the blade had sliced the femoral artery. The only thing that stopped him from dying from blood loss was the Weedle got to him first.
Larvitar uses a rock smash on Rico. Yes, a Pokemon can take that hit with only the risk of being knocked out. When Rico gets hit in the chest, it causes severe damage to his internal organs, and had Rico not been wearing armor, he would have died.
What does Issa do when his daughters start defying him in Here In My Arms? He withdraws their tuition from Youkai Academy so they have to come home. Tsukune even laments that for all the power he's gained, he still can't protect them from everything. Averted however when his familiar gives away a gem made from her fire to pay for their tuition.
The second act begins with (almost all of) the most powerful residents of Gensokyo meeting in order to fight a powerful new threat together, a common Fandom Specific Plot for Touhou fics. Turns out that a bunch of distrustful, violent megalomaniacs don't make the best alliances, and a combination of differing priorities, politics, and centuries-old grudges cause the union to fall apart before it began, the various factions and sub-factions either leaving or starting their own schemes.
Yukari assembles a dysfunctionalRagtag Bunch of Misfits, uniting them against a powerful enemy with massive odds stacked against them. They lose, horribly. Turns out going against a freaking Outer God was not her wisest course of action.
Hilariously in Never Gonna Learn My Lesson, Kurogane, Fai, Sakura and Syaoran aren't allowed to participate in the Piffle Firefly Race because they don't have any secondary education and have to pass an equivalency exam. And despite studying for a week, neither Fai nor Kurogane actually passed the test as they barely skimmed the surface of the topics they had to study and they succeeded due to Syaoran bribing the test administrator.
Despite being a skilled fighter, when Syaoran is jumped on his way back from the library in Shatterheart he gets his ass handed to him as 4 armed thugs to one unarmed man without backup are terrible odds.
Speaking of Syaoran's fighting skills, he noted to have a slower reaction time than his clone due to years of imprisonment atrophying his skills and not having the actual training.
When Syaoran and Kurogane suffer severe injuries such as Syaoran getting his knee shattered and Kurogane cutting off his own arm they spend months recovering from the injuries.
When Kurogane gets a concussion after having a roof fall on top of him he has most of his memories in tact, but doesn't remember the short amount of time that lead to his concussion as in most real cases of amnesia.
Braid of the Limbo Clone Squad. When he was facing his demise he was plucked from his universe by a mischief god and given his choice of powers. His choice: the natural laws of his Earth will always rule him. How does this count as a power? Well, the universe he was thrown into is an anime universe, meaning that the only reason the heroes haven't died is that the universe's laws seem to want to protect them. Which means he can see through the flimsy disguises that most people use and has no problem just killing the fuckers when they're not powered up with a simple sniper shot to the head.