In general, any episode where your preferred character dies will be this to at least a few people.
Any episode featuring two characters who would probably get along quite well under any other circumstance would qualify as this trope as well.
Especially to those familiar with their canon relationship, seeing the Teenage Mutant Ninja Turtles viciously murdering one another in cold blood is heartbreaking. The lingering pause on Leonardo's face when he collapses after finishing off Raphael is not the look of a winner; it is the face of horrible realization.
Goku vs Superman
Many whose childhoods went to Goku becomes this somewhere. Especially heartbreaking is the expression on his face and his Death Cry Echo as he's vaporised.
Their battle ended up completely destroying the planet Earth. Doubly so for Superman as he ended up destroying what he was sent to protect. His expression and the utter silence at the end of it all really hammers it home.
What's worse is just how petty it is. Superman never wanted the fight at all and Goku just wanted a good fight (and to stop what he thought was a possible alien threat), but unfortunately he and Goku just kept getting pushed to the point where they couldn't hold back anymore.
Mike Haggar's defeat at the hands of Zangief was this for Boomstick In-Universe. Possibly for Wizard as well, though he focuses on giving the post-battle explanation as he usually does and only joins Boomstick in mourning when asked by a fan if his preferred contestant ever ended up losing as a result of their research. Also Mike Haggar had a daughter and an entire city to watch over. This is a huge loss for both Jessica Haggar AND Metro City.
Felicia's defeat means that the orphans she cares for just lost their caretaker.
Really the case for any character who has a family/True Companions/In-universe Fanbase that ends up dying. Who knows how they'll react to the news to say nothing of Leonardo and his brothers...
Ash Ketchum won't be happy when he finds out about Pikachu's defeat at the hands of Blanka.
Presumably, Luigi goes after Tails because of Mario's death at the hands of Sonic. All he accomplishes is also getting killed and making a child a killer. On top of that, Peach survived her battle and must live without the protection or kindness of the brothers. Another layer there: Link lost Zelda in that fight. Yeesh.
Zelda and Link reincarnate. She'll be back. We should be more worried about Link, now armed with whatever Materia he looted from Cloud's corpse, stomping over to the Mushroom Kingdom and decapitating Peach. It leaves her kingdom leaderless and the Mushroom World short three of its seven Star Children.
It'll be worse if Bowser's abducted Peach when Link shows up. Why? Because then Link will hunt Bowser down to get to Peach. One, Bowser's affection for Peach is generally portrayed as genuine, meaning he'd be more than willing to fight Link in her defense. Two, Bowser has eight kids, all of which will either be orphaned or slaughtered as collateral damage in the hunt.
Fox McCloud vs. Bucky O'Hare is probably one of the most depressing match-ups to date. Fox loses one of his closest friends, Wiz and Boomstick see one of their favorite characters get blasted to smithereens, and Bucky loses just about everything. It's hard to say anyone actually won that fight.
Luigi vs. Tails: Although the episode has plenty of Funny Moments, it doesn't change the fact that it's a battle to the death between gaming's biggest Butt-Monkey who lost and an innocent kid no older than 11 who won. The worst part is that this all happened right after the Year of Luigi. Right after Luigi finally gets his time in the limelight, he gets defeated in a Death Battle.
The expression of sheer terror on Venusaur's face as it burns up in Charizard's flames.
The Pokemon were leveled up by rare candy instead of being already fully grown. Three kids just fought to the death.
The final scene of Tigerzord vs. Gundam Epyon is a mixture of this and cartoonish hilarity, but as always, thinking about this battle too hard is Harsher in Hindsight. Zechs/Milliardo is left without his lover and with serious emotional scars while Zordon just watched one of his peacekeepers explode along with 3 of their strongest weapons and is clearly affected by this. Meaning, in the end, no one truly won.
Kirby is quite clearly devastated after his Star Rod is destroyed. It's even worse after Buu launches his Planet Buster and Kirby looks up from crying with tears still in his eyes. He knows that he had to dig deep in a VERY short period of time to counter this. If one of the most powerful weapons in his canon and last moves, his Hypernova form, is thwarted by Buu, then his entire home will be vaporized in return. Really, the whole battle was a big tearjerker for poor Kirby and for anyone who cares about him. The levels of physical and mental pain he was exposed to, while basically being a blobby version of an innocent Kid Hero, is nothing to laugh about. We're basically seeing a young kid getting the tar beaten out him, seeing his home threatened and being brought down to his knees as he faces a Cruel and Unusual Death. Sure, he won in the end, but it's still pretty harsh in hindsight.
Guts' backstory is a combination of this and Nightmare Fuel. From being born from a woman hung from a tree during a massacre, to watching his surrogate mother (the whore of a mercenary band) die at age three, to being abused physically, emotionally, and sexually. And when he finally finds friends and a girlfriend, his best friend summons an army of demons who rip apart his friends while being force to watch said best friend (now a bird demon) raped his girlfriend, and then it turns out Casca was pregnant with his child, which was horrifically mutated by the rape. The poor guy just can't hope to catch a break.
Furthermore, Soul Edge has been shattered and Inferno vanquished before by the blade of Soul Calibur (its intended counter) itself multiple times, and it's always returned. Who's to say that the demonic blade won't just regenerate in time? It might not even take much time. Guts merely cleaves Soul Edge in half and shoots some crossbow bolts at it. It's been able to function just fine as two pieces. In all likelihood, Inferno will just wake up the moment some other poor shmuck picks one of them up. Slam the halves back together, then bam- Nightmare's back and Guts will likely be long-dead by that point.
Goku vs. Superman 2 ends with Superman softly, sincerely saying "I'm sorry" right before killing Goku quickly and painlessly with a heat vision bolt through the skull when Goku makes clear he's never going to stop fighting, even though he's clearly overpowered. The whole thing ends with Superman carrying Goku's body rather than letting him fall. Also, just like the first time, despite Death Battle's tendency of not caring about the heroes' no-kill policy, Superman was an exception; he tried to stop the fight non-lethally more than once, but was ultimately forced to kill Goku so he would not destroy the planet, noting how he was "too strong for his own good". At one point, Goku yelled to Superman, "Get off my planet!" meaning he still thought Superman was an alien invader.
Wolverine VS Raiden. Consider this: If Wolverine won, (which he didn't), Rosemary would have become a widow and John would be without a father. If Raiden won, (which he did), the X-Men would have lost one of their most valuable members, two of them if you remember Beast's defeat. So, whoever wins, at least one person will be losing someone very important to them.
Hercule Satan VS Dan Hibiki. Poor, poor Dan. The guy's father was killed, nothing ever seems to go right for him, and he's just so pathetic that it's natural to pity him. In his fight with Hercule, he sheds tears when he's about to lose, and he can only whimper "Ohhh mannn" before he suddenly gets killed by a jukebox suddenly exploding out from inside him- which was apparently unintentional on Mr. Satan's part. His death is pretty sad if you can get past the absurdity of it. To top it all off, when he's reunited with his father, he's disappointed in him. That's right- even in death, Dan can't do anything right. To add salt to the wound the crowd is explicitly cheering against Dan during the entirety of the fight. Dude was Chew Toy through and through.
Yang Xiao Long VS Tifa Lockhart ends with Yang giving a No-Holds-Barred Beatdown to Tifa, finishing her off by snapping her neck with the recoil from her Shotgun Gauntlets. After said horrific event, Tifa's broken and lifeless body is shown fading back into the Lifestream.
In the live stream for this episode, Barbara Dunkelman- Yang's voice actress- visibly flinched in horror at the deathblow.
Worth pointing out that this whole fight really reeks of tragedy. If Tifa won, which she didn't, Tifa would have killed a 17-year-old girl (a high-schooler) and the closest thing poor little Ruby has to a mother figure. If Yang won, which she did, Denzel would be an orphan again and Marlene would lose the closest thing she has to a mother figure, not to mention her, Aerith, and Cloud are Together in Death.
A case of Fridge Tearjerker but Monty did state that he was a fan of Final Fantasy VII and with the similarities between Tifa and Yang, it isn't hard to see Yang as at least a partial Expy of Tifa. Meaning Yang killed what could be considered her origin.
On the other hand, they're robots. Destruction is more of an inconvenience than a permanent solution. Heck, how many Robot Masters were destroyed only to be brought back?
Since Mega Man has his extra weaponry stolen from defeated (and killed) Robot Masters when he enters his fight against Astro Boy, this clearly means that, as the hosts stated before, made Mega Man extremely angry, as well as dangerous with violent outbursts of destruction and changes in personality. Put it in this perspective as the gaining of these weapons turns him from a high-spirited robo-boy version of Captain America, into a trigger-happy(/angry) violence-prone robo-boy version of Batman. With that in mind, Mega Man probably had just gone through a fight or two, has not cleared out his extra weaponry, and as such, became extremely violent and deadly, meaning that he found another robot looking down on a city, and probably thought to follow the part of his brain that might have thought that Astro Boy would be a threat, and, with his wires and processing filled with destructive power and anger,thought it best to just go up to the fellow robo-child, and start attacking him., WITHOUT REASON. All he knew at this point was to either go home and getting his extra abilities taken away and return to normal, or to keep fighting robots and bad guys, making him more violent, and likely to hurt someone in the process. The sad part in whole, is that he becomes basically evil almost, because he chooses to do so to protect others. Ironically sad in that he destroys evil, while becoming so.
Hawkeye's backstory is one traumatic moment after another. He and his brother were frequently beaten by their abusive drunk of a father, and were both orphaned when their parents died in a car crash. The man who adopted them was even worse than their biological parent, and tried to run them over in his truck. They were rescued by a pair of circus performers who took the Barton brothers under their wing and brought them to live and train at the Carson Carnival of Traveling Wonders... only for the two performers to turn out to be supervillains who were training Hawkeye's brother Barney to be a criminal as well. The deciding blow of the Green Arrow vs Hawkeye fight can be this if you know the significance of GA's diamond tipped arrow. He used it to free members of the Justice League in a move that got him accepted into the team. Then years later he would place the diamond on the engagement ring he would use to propose to his long time girlfriend Black Canary. It is shattered by Hawkeye's Adamantium-tip arrow before it kills him. And then Dinah is shown posing alongside Hawkeye.
Pokemon vs Digimon.
Regardless of who wins, two best friends will die. In this case, it was Red and Charizard. Wargreymon rips Mega Charizard X apart with his Dramon Killers while Tai beats the hell out of Red. Mega Charizard X falls on top of Red, accidentally breaking his legs. Then Wargreymon nukes them with Terra Force. Even worse, despite having his legs broken, being horribly roughed up, and about to be utterly incinerated, Red's final thoughts are of Charizard, not his own fate. While the bond between the two is mentioned to be one of master and pet rather than as equals in the analysis, it can't be said that Red didn't love Charizard.
Torrian's original idea was to not only have Red's legs broken, but to visibly show his bones sticking out of his legs.
Red thought they were having a friendly Pokémon battle and didn't learn that Tai and Greymon were willing to kill them until it was too late.
Just the final shot can send many Pokemon fans crying like kids again: the sight of Red and Mega Charizard X being reduced to ashes. Even worse was seeing Charizard try his hardest to resist but ultimately falling.
This battle can be jarring to those who grew up watching either show since they had a massive Fandom Rivalry back then. Just seeing the mon and trainer you saw grow and become stronger end up dying can leave a hole in your heart. This rivals Goku vs. Superman in that department.
Boomstick: Ow... my childhood...
Bayonetta vs Dante
The source of Bayonetta's powers is a contract she made with a demon named Madama Butterfly. In exchange for her powers, her soul is now forever condemned to eternal torture in Inferno from the moment she dies...which is exactly what happens after her gruesome death at Dante's hands. Madama Butterfly herself ends up having her leg sliced off before being nonchalantly decapitated by Dante. Bayonetta's voice cracks when she realizes her sponsor and the only friendly demon she knew has just been killed.
In the DBX battle of Trish VS Jeanne, we saw that Jeanne kills Trish. To make it worse, in the original Death Battle Bayonetta was killed by Dante, so both victors, Dante and Jeanne, lose an ally.
Bowser vs Ganondorf: Just the possibility that Bowser Jr. and the Koopalings might be left completely orphaned after having their father viciously murdered by someone as evil as Ganondorf is a thoroughly unpleasant one. Which ultimately does happen, also leaving the Mushroom Kingdom short of three of its seven Star Children. Then again, death for Bowser (and the Marioverse in general) seems to be more of a momentary inconvenience, so long as they have enough extra lives and/or 1UPs. Although a 1-Up probably doesn't act as insurance for having your body decay as part of a curse, then having what remains of your body blown to smithereens...
Flash vs Quicksilver: When the battle is over, Magneto appears to mourn his son's death.
Meta VS Carolina: In Season 13 of Red vs Blue Carolina explicitly states that she treated the other Freelancers as family and their deaths were the reason she didn't want to lose the Reds and Blues. Now she has to not only fight Maine but also try to kill him, which she actually does. However, listen closely to the lyrics of the music for the fight. "Grant the souls I send your way final peace and rest at last". Given the circumstances, it's safe to say Carolina is not only upset for having to try to kill him, but sees killing him as some sort of Mercy Kill given the Meta's unstable mental state. With that in mind, her execution of the Meta takes on a much more somber tone.
Cammy VS Sonya: Just the way Cammy thrashes in a desperate attempt to escape death— and similarly, in how despite being heroic in her intentions, what with trying to apprehend Kano without killing him and engaging Sonya on the basis that she used excessive force (by killing him when she was trying to arrest him alive), she's brutally murdered by Sonya as well without an inkling of remorse or humility.
Ken Masters VS Terry Bogard: This is a bout between two unquestionably good and friendly warriors with the purest of intentions. Just the idea of having them fight each other to the death, especially when both men have a very large network of family and friends, is upsetting. If Terry dies (which he didn't), he would suffer the same fate as his father— leaving Andy with no family left, costing Mary yet another close friend, and depriving young Rock of the closest thing he has to a parental figure. Likewise, if Ken dies (which he did), then Eliza will be left widowed, his son Mel will be left fatherless, and Gouken will have lost both of his students. So, in a sense— no matter who wins, a lot of people will be losing someone very close to them.
Amy Rose vs Ramona Flowers: After being knocked out cold to the prelude to the fight, Scott regains consciousness just in time to see Ramona unconscious and bloodied, and is understandably distraught. Mere seconds later, Amy then pancakes her with an arcade cabinet, leaving him borderline catatonic with grief.
Hulk vs Doomsday
After Wiz says The Hulk originally manifested as an imaginary friend for a young Bruce Banner, in the "Hulk" preview of the upcoming fight, Boom-stick mentions he too had an Imaginary Friend: he called him dad. Even Wiz is briefly at a loss for words, before moving on.
The ending. Here we have a definitely heroic Banner being shot into the fray by his Avengers teammates, as indicated by his drop pod, to stop Doomsday. He fails.
Roronoa Zoro vs Erza Scarlet: No matter who wins, either the Straw Hat Pirates or the Fairy Tail guild will lose a important member of the group and a friend (take in consideration that both One Piece and Fairy Tail works around the power of friendship). The Straw Hat Pirates didn't lose any member after the battle, while the Fairy Tail guild.
Lara Croft vs Nathan Drake: Many people will mourn Nathan Drake's death: his love interest Elena, his pathernal figure Sully, his friends Chloe and Cutter, and Sam will lose all the family he had left.
Scrooge McDuck vs Shovel Knight
This is a fight between two heroes who both have loved ones. If Scrooge dies (which he didn't), Huey, Dewey and Louie would be deprived of their uncle, who they care for a lot. If Shovel Knight dies (which he did}, Shield Knight will lose her one true love.
Due to the death of Shovel Knight, killed rather brutally and with his bloodied head put up on display as a warning to prospective thieves, Huey, Dewey and Louie are going to have to live with the fact that their Uncle Scrooge is a murderer.
Venom vs. Bane
The look on Batman's face when he sees Bane's headless body. You can practically hear Kevin Conroy's horrified "No..." seeing one of his greatest adversaries murdered so easily.
As Boomstick notes, life has not been kind to Eddie Brock. Eddie spent his entire life trying to gain approval from his father who blamed him for Eddie's mother dying in childbirth. However during his big break, where he revealed the identity of the serial killer known as Sin Eater, Spider-Man caught the "real" killer (when Carnage is inverted it is revealed that Eddie was right) which resulted in him getting publicly humiliated, fired, divorced from his wife and disowned by his father. Eddie would then go on to learn that he had cancer and went to church to apologize to God because he was about to commit suicide, only for him to bond with the Venom symbiote instead. It was an experience so traumatic that he cries whenever a symbiote starts to bond to him again. Unlike Bane, Eddie does not do any villainous acts besides trying to kill Spider-Man and after forming a truce with Spider-Man, he would go on to become an anti-hero.
Power Rangers vs. Voltron Force
Whoever wins, at least 1 group of 5 best friends will die. It's the Power Rangers, who face a common end in being blown up by Voltron. The silver lining here is that they were all Together in Death, especially if you remember that Tommy died at the hands of Epyon.
Double whammy given the red lion was cut off from the main body and we don't hear anything out of Lance after a scream. It was assumed by many fans that Lance had been killed in action, made worse by how truly furious Pidge was after his sacrifice. While it would be confirmed in the following week's Death Battle Cast that he did survive (with the scene confirming his survival being cut due to time restraints), the winning team still came uncomfortably close to tragedy.
More of a meta tongue-in-cheek example, but due to the casting, PBG and Jeff were unironically trying to kill each other.
Natsu vs. Ace: Regardless of who wins somebody is losing their brother. By the end of it, the Fairy Tail guild avoids losing a valued member of their family, but the Whitebeard Pirates, Luffy, and Sabo have lost a brother for the second time.
Android 18 vs. Captain Marvel
Boomstick opens up a cold one for Mar-Vell, the original Captain Marvel, upon his death.
If Android 18 dies (which she didn't), Krillin and Marron would be left without a wife and mother respectively.
Captain Marvel's defeat is sad for a couple of reasons... but with the top reason being now, she's with her boyfriend, James Rhodes, aka War Machine, who in the current comics, died.
Smokey Bear vs. McGruff the Crime Dog
Smokey's backstory has a tragic overlap with the real world. Only a few years after Smokey was originally created as a mascot, a particularly vicious wildfire broke out in New Mexico, where thousands of forest creatures either lost their home or died. Among them was a small American Black Bear cub, who was found clinging with burnt paws to a smoldering tree, having lost his parents in the blaze. This cub was rescued by firefighters, eventually named Smokey after the mascot, and became the real-world incarnation of everything the cartoon bear stood for. While it's a triumphant ending to a heartbreaking tragedy, the hosts are understandably somber while they share the story.
While discussing that McGruff doesn't actually hold a rank in the police force, Boomstick takes a moment to remember a dog that actually held an official rank— Thailand's Air Chief Marshall (true story), Fufu.
Boomstick: Rest in peace, buddy.
McGruff's last words really do tug the heartstrings—
Either the Avengers or the Justice League will wind up losing a very important member in this fight. Thor wound up losing, which means the Avengers lost a teammate & a friend, Jane her lover, Asgard their hero and Odin his son.
Naruto vs. Ichigo
No matter who wins, a beloved hero and friend will have been lost. In this case, it's Ichigo, meaning that Isshin, Karin, and Yuzu lose another family member, Orihime loses her lover, and depending on whether this takes place before or after Kazui is born, he'll either end up without a father, or have never existed at all.
On that note, had Naruto lost, it's very clear that this is Shippuden-era Naruto, meaning that not only would he have failed to achieve his dream of becoming a Hokage, but Hinata would lose her future husband and Boruto and Himawari would never have been born.
Sephiroth vs. Vergil
Vergil's final moments. He manages to use Yamato to cut through dimensions and escape Sephiroth's Supernova, but is severely damaged. When he gets out, he sounds relieved, but is then abruptly killed by Sephiroth.
Vergil: I'm... free...
Sephiroth: (impales Vergil on Masamune from behind, causing him to drop Yamato) Hm. So youare.
Twilight inadvertently made her unleash her Dark Raven form that she despises so much; is it any wonder the pedestal is broken?
The end of the Raven preview show that Wiz and Boomstick do not want to deal with another pony. Seeing as the last time they had a pony on the show, she and her opponent broke the fourth wall and the rules, they very much are dreading this one. Thankfully for them, it goes normally.
The start of the battle shows the Golden Oak Library getting burned down again, after seemingly having been rebuilt after it got destroyed. As if it wasn't enough that Twilight has to fight for her life...
By extension, just the fact that two of the PlayStation's Killer Apps are going at it in a fight to the death. At least one 90's kid is going to have their childhood destroyed.
The reason these two are even fighting? Crash squashed Spyro's adoptive brother Sparx, assuming him to be an average annoying insect. Spyro's horror as he realises what the Bandicoot has done really sells it:
The conclusion is essentially a Downer Ending. Not only has Coco lost her brother, Crunch his adoptive brother, and Aku Aku his son, but Spyro turned into Dark Spyro — which, much like with Guts and his Berserker Armor back in Season 2 — he cannot change back from without outside assistance. With Sparx dead, Spyro may be unable to revert back to normal.
Cynder at least is still around, so maybe Spyro will come back — which does alleviate this a little. Then again, Sparx is still gone, and Aku Aku dies trying to protect Crash in what ultimately amounts to a Senseless Sacrifice, which is still pretty sad.
Despite the undeniable badassery of both combatants, the fact still remains that they're both AdorkableKid Heroes with strong loyalties to their friends and loved ones. Regardless of who dies, it'll still be painful.
If Pit dies, the outcome probably won't be so severe, as it's been established that Pit's come back from all his Game Overs in the past — though he has come close to being Killed Off for Real at least once. Sora, on the other hand, has no such luck. And even without Pit's "come back after dying" fallacy, Sora's death will hit the hardest since he'd be leaving behind Riku, Kairi, Mickey, Donald, Goofy, Jiminy, Chip, Dale, Yen Sid, Lea, and every other friend he's ever met. Not only that, but that also ensures the deaths of Roxas, Xion, and Ventus, considering they all technically live on as a part of Sora's heart.