While it's not been seen in canon, fanon sometimes makes England this towards America. When not pairing them up, that is.
Oga from Beelzebub seems to not care for Beel, but, if you put a finger on the baby... In chapter 107 he openly declares himself to be Beel's parent, emphasizing this trope even more.
Guts from Berserk acts like this toward the Cute Witch Schierke, and toward his True Companions in general. Ironically, he doesn't act too much like this toward his insinuated son, the mysterious Moonchild, but most likely because Casca won't let Guts near the little boy or because whenever the Child does appear, larger than normal battle shit happens and they never spend any "quality" time together. However, when the latter happens, the roles get switched.
Black Cat. Have some nefarious scheme for Eve? Want to study the nanomachines that she uses? Feeling compelled to dissect her just because you can? Pray to the god of every religion you've ever known that Train and Sven don't find out about it. Especially the former of the two.
Don't so much as think of threatening Pinoko or Black Jack will cut you to ribbons. Then sew you back up. Then charge you everything you're worth for the trouble... Yeah, it's just that kind of story.
Also, when a child's life is in danger, expect Black Jack to work even harder for the kid's sake. Or to deal even harsher gambits in an attempt to make others empathize with said kid.
Ginji Matsuzaki. Do not even look at his protégé Yukio wrong, or this badass swordsman will cut you down. Ask about what he did to Chaka, to start...
Rokuro Okajima aka Rock. As seen with Gretel, Garcia, and later, Yukio, he'll go to great lengths to shelter children and teenagers from harm. Kidnapping and then molesting and abusing Yukio is a good way to make this usually mild-mannered, diplomatic and well-spoken former Salaryman angry enough to actually cuss you out and physically assault you.
Bleach: When Nnoitra threatens Yachiru, she warns him Kenpachi will be angry. Kenpachi dismisses it, but when Nnoitra does try to kill Yachiru, Kenpachi leaps into action. Later, when Yachiru is at Gremmy's mercy, he's interrupted from killing her by Kenpachi who admits he only turned up because Yachiru's reiatsu had become very weak.
Daikichi from Bunny Drop makes for a realistic example, by adopting a 6 year old no one wanted to take responsibility for, and doing whatever it takes just to make sure she gets a decent childhood. Commander Badass would be proud.
A Certain Magical Index: Have you harmed or threatened Last Order? If yes, then you are a dead man walking. The only question is how much of your body will remain after Accelerator annihilates you.
Whenever he learns that his daughter Ran Mouri and/or his charge Conan Edogawa are or have been in danger, Detective Conan's KogoroMouri is definitely not pleased. And you do NOT want to provoke a man who looks and acts like a slob, yet is a National-level judoka andacts at his most competent when It's Personal. More than one suspect has been at the receiving end of a powerful judo throw for this.
Inspector Juzo Megure is also very protective of the kids who hang out with Mouri and of his own subordinates. Better shown when he goes It's Personal mode in a case involving young women being attacked: he refuses to let Action Girl Satou act as a decoy once his Berserk Button was pressed, and later took a metal pipe to his head while protecting Sonoko from the culprit. It's explained that this comes from one of his first cases, where he failed to protect a schoolgirl posing as a decoy and she almost died. Fortunately, the girl got better... and then they gotHappily Married.
While there are many Papa Wolves and Mama Bears among the Sympathetic Murderers, there was a specially dark take on this trope during a two-part anime only episode. A businessman named Ushio Bunzou had contacted Kogoro to locate an assassin whom he had hired to kill him, having backed off the deal but not being able to find him and tell him so. It turned out that Bunzou was using Kogoro and others in a Batman Gambit destined to find and kill said hitman with his own hands, since one of his assassinations jobs led to the accidental death of the tycoon's beloved daughter Chisato. Conan had to beg the grieving and very pissed off Bunzou to not exact said revenge and damn himself in the name of his little girl, but he also made sure that the hitman's threat was neutralised and he was taken into custody.
Dragon Ball and its sequels have a lot of dads, but the grand master of this trope is Piccolo, to the point where his constant and epically badass rescues of his pupil Gohan become something of a Running Gag.
Despite wanting nothing to do with Future Trunks (usually ignoring him or just pushing him aside whenever Trunks tried to reach out to him), Vegeta wentcrazy after Cell killed Trunks.
"How could I let this happen to my son? He has sacrificed everything for me and I have done nothing but ignore him. I won’t give up on him! There is still time to change things. Cell has crossed me for the last time! He has tricked me in battle, mocked my Saiyan ancestry, but this! This time he has gone too far! He will pay the ultimate price for what he has done to my son!"
Vegeta willingly kills himself trying to take Majin Buu down with him, all for the purpose of saving his son's life, knowing he would go to Hell afterwards for all of the terrible things he had done in his life. In Vegeta's mind, Trunks was worth it.
The Non-Serial MovieBojack Unbound has Goku, despite being dead, attacking Big Bad Bojack for trying to Bear Hug Gohan to death. And he succeeded, giving Gohan the encouragement and strength he needed to win.
Throughout the movie, Vegeta appeared to have lost his passion for fighting since Goku died, not even watching the competition. But when Trunks was in danger, he immediately sensed something was wrong and headed to the battlefield, making a Big Damn Heroes moment to help Trunks out of a tight spot.
An old man in the episode "Free the Future". While Android 18 was blowing things up after getting angered with Android 17 for killing a boy she thought was cute, the old man attempted to shoot Android 17 (as that boy was in fact his son). It failed, because Android 17 was resistant to gunfire, and needed saving by the time Trunks arrived.
This is also inverted, as there's a common theme throughout the show where whenever Goku or Piccolo is in immediate, life-threatening peril, Gohan snaps and proceeds to kick the bad guy around until the latter stops moving.
When a traumatized and nearly dead Future Trunks reappears in the present timeline of Dragon Ball Super, Vegeta's reaction crosses somewhere between shock and outright enraged that someone went after his son. And once Vegeta finds out exactly what Black Goku has done to his Future wife and son, he's more than willing to rip himto pieces.
In Super we see that Gohan grows up to become one himself to little Pan. Doctor fake evidence of him cheating on his wife in an attempt to break your marriage up? He gets nervous and tries to explain, but not angry. Start getting noisy enough to disturb his daughter and he'll "politely" escort you across the room and ask you to leave. Kidnap his daughter and you're just asking for it. Gohan outright says that the only reason he wouldn't let Jaco kill Barry Kahn was because Pan was watching, and he didn't want her to witness death at a young age the way he did.
One of the weirdest (andthat'ssayingitNICELY) examples ever is Dr. Shingen Kishitani from Durarara!!. In the novels, we learn that Shingen was the one who cut Celty's head off and sold Saika's sword off to the Sonoharas... but he did it in order to protect his young son Shinra from Namie Yagiri's grandfather, who threatened to kill Shinra if he didn't.
Fairy Tail: You can do anything to him, even completely destroy his guild and Makarov will only get irritated, but if you hurt any of his guild members, there's a very good chance he will make you stop breathing.
In the second OAV based on the video game Fatal Fury, titled FATAL FURY 2: THE NEW BATTLE, lead hero/fighter Terry "The Wolf" Bogard has lost his will to fight and live after being beaten by Wolfgang Krauser, only to have a street kid named Tony tag along with him. Tony, who lost his father in a street fight and works as a shoe shine-boy to support his mom Elsa, worships Terry's reputation as a fighter and wants to be his disciple. After the defeat, Terry spends half the special getting drunk and not caring about anything... It is only after Axel Hawk, the heavyweight boxing champion of the world, orders his sparring partner to beat Tony within an inch of his life in a bar (after Terry drunkenly refused to fight Hawk when challenged), does Terry rise out of his funk...and drops Hawk with ONE PUNCH. Even Hawk can't believe it (as his inner narration mentions).
In The Movie, Kim Kaphwan gets to show off his Papa Wolf credentials as well. When a Brainwashed and Crazy Cheng Sinzan steps into a party he's attending with the main cast and his family, Kim offers to fight him so his two kids can see him kick ass. His rival, however, soon starts wiping the floor with him, so much that Joe has to be stopped by Andy from breaking in... but the very moment one of the Kim boys begs his daddy to not lose, Kim brings himself back and completely curb stomps his enemy with a single Ho-oh Kyaku.
There's an interesting straight use and subversion of this trope, pulled off by the same character (a villain). He's the leader of a wolf-themed gang, and one of their raiding parties gets their asses handed to them by Kenshiro. When he finds the bodies, he howls for vengeance, taking the rest of the pack with him to hunt for Kenshiro. The subversion comes from the fact that when they are utterly defeated by Kenshiro and Rei, one of the midgets in his gang comes up to him and asks for help. He tells him to get lost, that he can start a new pack anytime he wants. Then they all die.
In Fruits Basket, we have Kazuma Sohma, uncle and foster father to Kyo Sohma. In one chapter of the manga, Kazuma proclaims his intent to protect Kyo single-handedly from the entire Sohma family if he must.
There's also a sketch in one of the later volumes, where Kazuma meets with Kyo's Jerkass of a father, cheerfully telling him that now that the Zodiac curse has been broken and Kyo is free, it's time they had a little talk about Kyo's future. Kyo's father looks like he's pissing himself in fear. It's Played for Laughs, but given the psychological abuse the father heaped on Kyo (at one point he accuses Kyo of trying to kill him for standing too close to him), it's very much impressive.
Fullmetal Alchemist: "Don't EVER mock my son." Screw with Hohenheim's kids and you're in trouble. Not only that, but he's willing to sacrifice his own life to bring his youngest son Al back from the Gate, and when asked by Ed why would he do such a thing, he calmly replies, "Because I'm your father".
Maes Hughes also counts, telling several party-going toddlers not to "try anything" with his daughter. Complete with Scary Shiny Glasses and Dramatic Gun Cock. It's Played for Laughs, but you know that if anyone ever really did threaten his beloved Elicia, there'd be hell to pay.
Gintoki is this to Kagura and Shinpachi...sometimes.
Umibozu is also this to Kagura (he's her real dad) and becomes this to Kamui when facing Utsuro.
(in a letter to Kagura) If anything happens, all you need to do is send me a letter. I'll go over there and kill everybody.
The titular Onizuka from Great Teacher Onizuka who goes through great lengths to protect his students. In fact, you don't even have to be his student. He will rescue you anyways. This includes getting shot multiple times in an attempt to rescue a school girl (who happened to be trying to discredit him as a teacher) he saw being kidnapped while on his way to take an exam.
Kokkuri the Papa Fox, naturally, as he frequently worries about Kohina's wellbeing and safety (her poor eating habits are what convinces him to look after her in the first place).
Shigaraki the Papa Tanuki as well, surprisingly enough. Despite his mischievous and laidback nature, he likes to take good care of children and protects Kohina from her pet cyclops when it tries to kill her in her sleep.
Brandon 'Beyond the Grave' Heat from Gungrave, both in the anime and the game. He is extremely protective of Mika, a thirteen-year-old girl who is the posthumous child of his boss and his ex-lover. In the very first episode, Grave wakes up from his hibernation (it's been over thirteen years since his hibernation) to kick ass not because of being activated by the doctor; instead, it's because he hears Mika's scream.
During the encounter with Bunji, Grave has been shot several times with Anti-Necrolyzed bullets and crippled. He only has his left arm intact and Bunji is already pointing his gun at his head. But then, Bunji is annoyed by Mika, who begs him to stop. Annoyed, Bunjifires some misdirected shots at Mika, who is terrified. Seeing this, Grave snaps, gets up, and gives Bunji a No-Holds-Barred Beatdown by pinning him to the ground with his knees and beating him up with an arm. While shedding Manly Tears and what may be Berserker Tears (as revealed by Mika later). He stops when Mika asks him to stop.
Big Daddy is one to Brandon. When Brandon is shot to protect him from a Lightning agent, he snaps at Randy (who is worried about him) and tells him to call an ambulance to save Brandon first. Later, Big Daddy is grief-stricken when Brandon is murdered by Harry. And he is especially upset when he finds that Doctor Tokioka necrolyzes Brandon (even if it's Brandon's request because he wants to deal with Harry in case Harry veers off-course, which Big Daddy has known from Brandon's letter). He cries when he spends some moment talking to a hibernating Brandon and tells him to just rest in peace. After that, he decks Doctor Tokioka with a punch for necrolyzing Brandon without his knowledge before going off to confront Harry.
While not a biological father, Sousou/Cao Cao from Ikki Tousen is this towards his friends. So much, that his Superpowered Evil Side took full control of him whenever he saw them in danger. It first happened with his Unlucky Childhood Friend Chuukou (he thought the bullies at their judo club were attempting to rape her), and later with his Bash Brother Kakouton (who lost his eye while shielding him)). And in the anime series, he also recruited Myousai by protecting her from a rapist and offering her a chance to be his subordinate and fighter instead of a Child Soldier.
Sesshoumaru from InuYasha usually doesn't get too excited about much. Threaten Rin, though, and a beatdown like none other will commence. The best example comes from the manga... when Rin is taken to the underworld by a hellhound, Sesshoumaru follows and kills it. When she is already dead, whoops the King of Hell's ass to get her back. When this doesn't work, he actually shows the closest thing to human emotion he's ever done in the series, purifies the souls of the dead as an afterthought, then rips a hole back into normal reality. After all of this, his youkai queen mother acknowledges this and uses her powers to resurrect Rin since Sesshoumaru, of all people, is clearly unhappy about her death. He goes from Aloof Big Brother to a combination of John Creasy, Jesus, and Spawn.
Sai Nanohara from Jubei-chan is almost always a Bumbling Dad, but once he learns that his daughter Jiyu is the reincarnation and Soul Jar of Yagyu Jubei, he decides to not stay aside and does what he can to help her. In fact, his first Papa Wolf act was calling out Yagyu Jubei himself upon his treatment of Jiyu. To Jubei's very face. And in the Grand Finale of the first season, Sai also manages to give Jiyu/Jubei a Cooldown Hug to dispossess her from Jubei's influence, putting himself at great risk to do so.
Henry Marker from Karin is usually a weak-willed Bumbling Dad, but when his daughter Karin is in trouble, he will literally let himself burn in the broad daylight to rescue her from the well-intentioned but ignorant hospital people who think she's an Ill Girl, but could potentially discover that she's a vampire.
Most people try to kill vampires with stakes. Henry uses uprooted trees.
Kenichi: The Mightiest Disciple gives us a number of examples. The most prominent ones are Hayato Furinji, who's a Grandpa Wolf for his biological granddaughter Miu and also for Kenichi to a degree; Sakaki Shio and Apachai Hopachai, two of the Ryozanpakou masters who train Kenichi and will go all-out to protect him if he's in serious trouble; and most recently the Big Bad himself, Saiga Furinji, who joined Kenichi's group in disguise to rescue the kidnapped Miu, his daughter.
Not to mention Kenichi's father, Mototsugu Shirahima, who, when he found out just how brutal Kenichi's Training from Hell was, tried to escape with Kenichi from the masters. He even tried to save his son from a boulder that was rocketing towards them, regardless how futile it was.
Haruka's grandfather Zenzou in Kotoura-san can be violently protective of her granddaughter, despite being a Pervert Dad as well—He's the first person to stand by her as she's being rejected by the society for her telepathy. The word society includes his daughter Kumiko, or Haruka's mother. In fact, he disowned Kumiko as the latter disowned Haruka, and when he comes across her again some 10 years later, the first thing out of his mouth is a warning that he never wanted to see her again. The two only reconciled as Kumiko and Haruka reconcile. When he first meets Moritani in episode 6, he implies quite clearly that he knows what she did to Harukanote (She asked thugs to attack Haruka's Understanding Boyfriend Manabe, which indirectly broke Haruka out of Hope Is Scary.) and that she isn't off the hook with him.
Despite being the hero of Lone Wolf and Cub, Ogami Itto averts this trope. He considers his four-year old son to be something more akin to a True Companion than a child in need of protection. While he will walk through hell to help his battle buddy, as any samurai should, death in the line of duty is a professional hazard, and not something to be shied away from. Not even if you're four.
They may have marital problems in Macross 7, but don't ever think of threatening any of their children or their city or their ship; coz when Mama Bear Milia and Papa Wolf Max Jenius team up, you are definitely screwed. Especially emphasized on their killer combo attack in Super Robot Wars Alpha 3 as seen here.
Shy and helpful Ugo in Magi – Labyrinth of Magic becomes this when his friend Aladdin is threatened or about to be harmed. Best shown in his fight against Judar where he refused to return to his flute to protect Aladdin because Judar gleefully stated he would kill Aladdin for the fun of it. And for all purposes, he was arguably the closest thing Aladdin had to a father when Aladdin's dying mother asked him to look after her son.
Negi Springfield of Mahou Sensei Negima!, despite being four or five years younger than his charges. Threaten his students, and he will pull the spear you impaled him on out of his chest and beat you half to death with it.
Takahata is this way as well, but to Asuna in particular he's an adoptive father. Although only because his self esteem is too low to be her boyfriend.
It is implied at first, then outright stated, that Nagi and later Negi saved the world because it was the only way to save Asuna, an Artificial Human girl who was used as a Barrier Maiden and, in the past, horribly treated by those who kept her prisoner and used her Anti-Magic powers for their own benefit.
Not even a freaking typhoon could stop Kenzan Takakura from getting medical attention for his ill daughter Himari. And he still had enough pluck to shield one of his sons, Kanba, from a falling lamp. And had his other son Shouma been there, he would've protect the kid too.
Kenzo Kabuto from Mazinger Z and Great Mazinger. It is arguable if he wasor was nota good father. It is not arguable when his older biological son was about of being killed he sent a Humongous Mecha after the people was attacking him, and when his adoptive son was about of being killed, he blew his assailant and himself up. Therefore, althought his parental skills left much to be desired, you DON´T try to hurt his sons.
Danbei Makiba from UFO Robo Grendizer. If he thinks you are going to hurt his daughter, he WILL hang you with his bare hands. Or shoot your brains out (the only reason Kouji and Duke are alive is because his aim is awful). If he entrusts you to drive his daughter somewhere he'll load his shotgun in front of you as he warns she BETTER does not get harm in any way, shape or form.
Despite being the youngest (male) of the group, Mobile Suit Gundam 00's Setsuna F. Seiei is quite the Papa Wolf for his teammates in season two. This is so pronounced that sensing his comrades all on the brink of death pissed him off to the point that he unknowingly initiates the "Trans-AM burst mode", completely turning the tide of the battle.
An ironic example is Sergei Smirnov, who has been called ''Papa Bear'' (because in-universe he's nicknamed "the Wild Bear of Russia") by fans with the description of Papa Wolf in mind. He did fit the Papa Bear description given above regarding his treatment of his son Andrei, but with Soma Peries he was Papa Bear all the way.
All Might is already rightfully feared amongst the Villains of My Hero Academia. Mess with his students though, and you will learn just what his philosophy of "Plus Ultra" means in the most painful way possible.
Minato Namikaze aka the Fourth Hokage from Naruto. In fact, the whole deal with the Kyuubi has just recently been revealed as the struggle between him and Tobi, with Tobi using Minato's love for his wife/partnerKushina (then-host of the Nine-tailed fox) and their newborn son Naruto (future host of the same Fox) for his advantage. And we already knowhow THAT ended...
Hizashi Hyuga deserves a mention here, as the mere realization that his son Neji is a member of the Branch Family sends him into a murderous rage (which is stopped before it can begin courtesy of Hiashi activating his curse seal - and doing so is the first step in causing Neji to spend at least nine years of his life afterward as the inversion of this trope!)
Also Hiashi for killing that Cloud ninja for attempting to kidnap Hinata.
Maito Dai, Gai's father, certainly seems to count in Gai's flashback. Despite being known as "the eternal Genin", he follows/finds Gai's team while they're being cornered by the Seven Swordsmen of the Mist and unlocks the Eight Gates, killing himself to protect his son.
One Piece has Captain Whitebeard, formerly one of the four most powerful pirates in the world. An attack on one of the Whitebeard Pirates is never forgiven and his reactions are legendary-when the World Government sentenced his adoptive son and lieutenant Ace to death, everyone involved knew immediately that it was effectively an outright declaration of war.
After Ace's death, instead of going insane with rage like most had expected, Whitebeard in a frightful and calm way defeated his very powerful murderer Akainu in two blows and, in the same blow, split the entire Marine island in half... despite being stabbed, blown up, gutted and with half his face burnt off. All to avenge poor Ace's death. And you thought Whitebeard on a rampage was bad?
Shanks, when Luffy is threatened. There is a reason why he lost that arm of his...
Luffy himself is a version of this trope, as any attack on the physical or emotional well-being of his crewmembers is taken personally and likely to result in an angry and violent beatdown, like he did when Nami had a hertbreaking Heroic B.S.O.D. once her efforts to save her village were thwarted by her Bad Boss and he epically beat up and defeated said boss. Prior to the Time Skip, however, he was just a fledgling, made clear from the fact that he wasn't quite strong enough to back up this fierce protective instinct yet. He found that out the hard way in Shabaody, where the entire crew was more or less beaten half to death and scattered to the four corners of the Earth by Bartholomew Kuma and he was helpless to stop it. But especially, considering the fact that Kuma was on their side, that was nothing compared to when he went to The Alcatraz and then the World Government's headquarters to rescue his older brother from execution, only to have him die in his arms. Seriously, if he hadn't had Jinbe there to knock some sense into him, he wouldn't have been able to Take A Level In Badass to transcend pretty much all the limitations he had, and then some.
Zoro, too. He's normally not the type to take revenge. But Ohm made him reconsider that when he set traps that brutally injured Chopper. Also, when Robin was almost killed by Enel, he caught her before she fell (despite his earlier distrust against her) and furiously attacked Enel as a result. In fact, any member of the Straw Hats will beat up anyone who dares to hurt their True Companions, as proven when the Franky Family beat up Usopp, and the remaining male members returned the favour and destroyed their house in retaliation.
Garp is a Grandpa Wolf who would have killed Akainu for killing Ace if Sengoku, the Fleet Admiral, hadn't stopped him. He even tells Sengoku to keep him down or he would have tore Akainu to pieces.
Also, Luffy's actual father Dragon the Revolutionary has appeared only once or twice, but one of these apparitions puts him squarely here. When Luffy was about to be arrested by Smoker... Dragon shows up and keeps him from using his weapon. Then a gust of green wind blows through the island, freeing Luffy from Smoker's clutches. It hasn't yet been revealed if the wind was Dragon's doing, but...
Smoker himself acts as a Papa Wolf to his subordinates, especially Tashigi. He doesn't hesitate jumping in to save Tashigi and his men from Trafalgar Law telling them to run away and taking him on his own. Also he was really worried and shocked about his men when they get caught in a huge explosion. Then, when he finds out Vergo attacked them, he lays a beat down on him, and allows himself to lose their battle, in order to get Law back his heart, who has major issues with Vergo from the past. In short, you do not screw with the men under Smoker "The White Hunter", or you will regret it.
Kyros is one of the few on this list who is a literal father. While he's a toy, he protects his daughter from threats as extreme as kidnappers to as minor as boys asking her out, but once he becomes a human again and encounters her fighting Diamante, the man who murdered his wife, he gets pissed. The only reason he doesn't just smash Diamante there and then is because Diamante is targeting Rebecca with all of his attacks, but once Robin shows up to protect her, he can focus entirely on Diamante who, despite raining spiked balls onto Kyros, is one-shot by the man.
Trafalgar Law had one in Corazon, aka Donquixote Rocinante, Donflamingo's younger brother. The man spent six months trying to find a cure for Law's Amber Lead poisoning, and when doctors who foolishly thought it was contagious refused to treat the dying kid, Corazon beat them up and destroyed their hospitals. He later died to save Law's life, finding him a cure and engineering his escape from Donflamingo at the same time.
The OYAJI, from the manga of the same name, is a bloody extreme example of this. We dare you.....No, we DOUBLE DARE you to lay a finger on anyone in his family!
The last time two yakuza members tried to burn his family alive, their whole gang ended up being massacred in the most brutal way possible and then burnt to ash! The scary part? This was done right in their own base by the old man with a shovel all lone!
Heck! Even his would-be son-in-law learned this in a very,verypainful way!
Plastic Memories subverts this in Episode 5. When Michiru's adoptive father becomes a Wanderer, he goes crazy after hearing Michiru cry as a R-Security soldier tries to forcibly takes her away from him. Unfortunately he then starts targeting Michiru after he "saved" her, and is only stopped after being brutally gunned down.
Gesicht: Even if the world ends, I won't let you go.
James of Pokémon fame is rather protective of his Pokémon in the Sinnoh arc, especially Mime Jr. (which is a baby Pokemon, by the way). Sometimes he goes as far as teaming up with Ash and company just to keep them safe. Oh, and when Jessie and Meowth refused to help out one of those times, he attacked them.
Ash himself counts too. Countless times, he has put his life on the line without hesitation to save his Pokemon. And for that matter, Ash's Pokemon can be fiercely protective of their owner... Just ask his Grovyle, who had been Brought Down to Normal due to an Heroic B.S.O.D., but recovered his powers out of sheer willpower upon seeing Ash in lethal danger!
In Pokémon Heroes, Latios is a Brother Wolf to Latias. He refuses to let any strangers into their secret garden, and is even willing to sacrifice his life just so his sister and the town of Alto Mare could be safe.
Psycho-Pass: Tomomi Masaoka may be the oldest Enforcer in Division 1, a latent criminal and a chronic alcoholic besides, but threaten his son Nobuchika Ginoza and you'll see firsthand that he has 30+ years of combat experience for a very good reason.
Tendo Soun of Ranma ˝ isn't as badass as most of the cast, but disrespect any of his three little girls and you'll realize that he hasn't forgotten much of Happosai's Training from Hell. Saotome Genma, on the other hand, is cursed to transform into a literal "Papa (panda) bear". See the opening statement on why this trope is named "Papa Wolf" and not "Papa Bear" and you'll understand the Fanon that Jusenkyo curses are Personality Powers.
Deconstructed in Rash: when he saw his daughter Misaki attacked by her Stalker with a Crush Akiyama, Toshinori Ogata beat him to a pulp with a baseball bat... And was arrested and sent to jail for assault, as the judge determined he had gone overboard. Worse, the judge decided that Akiyama could not understand what he was doing and thus gave him a lesser prison term, resulting in Akiyama being freed first a few days before Misaki would marry another man, stealing a picture from her home, visiting Ogata in jail to make him know he was around, and then try and murder Misaki.
Kenshin, however, manages to reconstruct the trope and play it straight. When he fell through the Despair Event Horizon due to believing that his girlfriend Kaoru had been massacred by Enishi and his group, what brought him back to his senses was Yahiko's girlfriend Tsubame telling him that Yahiko was fighting Enishi's group alone. Few later, Kenshin pulls a massive Big Damn Heroes to save Yahiko.
In the Street Fighter IV OAV The Ties that Bind, none other than Ken Masters becomes this. With good reason: his wife Eliza has been abducted by Crimson Viper, and then he learns that she's pregnant. This is so awesome from his part that Viper herself notes that the massive fighting power he displayed was no slouch compared with none other than Ryu's Satsui no Hado. (And might as well be the Power of Nothingness that opposes said SNH); considering how cheerful and cocky the dude is, it puts on perspective how fucking pissed off he was.
Kotetsu T. Kaburagi of Tiger & Bunny may have a strained relationship with his daughter, Kaede, due to his job as a superhero (which she isn't aware of) meaning that he has to spend a lot of time away from home, but he's not about to let anything harm his little girl. This is showcased when he lifts a collapsed tree to save Kaede from a collapsing shrine even when his powers run out, and later, when Maverick has a gun to Kaede's head, Kotetsu reveals himself to be Not Quite Dead and punches Maverick in the face.
Yoshimura turns out to be one, in an incredibly tragic way. The organization he once served wants nothing more than to kill his beloved daughter. To keep her safe, he left her in the 24th Ward and avoided all contact to prevent them from using him to find her. When he learned of her rampages as the One-Eyed Owl, and found out she had been wounded in battle, he impersonated her to throw all pursuers off her trail. He has spent the last decade Taking the Heat for her, and when given one last chance to save himself (and Anteiku), he throws it back in their face by denying having a child. All this clearly kills him inside, but even her being the Big Bad of the series does not diminish his devotion towards keeping his daughter safe.
In the sequel, Haise Sasaki is one towards his squad. When Orochi tries to kill them, he unleashes a brutal Curb-Stomp Battle that leaves them all speechless in shock. Though only a few years their senior, he is a fiercely protective Parental Substitute to them.
Mirumo Tsukiyama is a Doting Parent to his only son, Shuu. But when his beloved son is in danger, Papa reminds everyone that Asskicking Equals Authority in the Ghoul world. When the family is targeted for extermination, he first uses himself as a decoy to allow servants to smuggle his son to safety. When this ploy ends in failure, Mirumo decides to escape and come help — while he plays it off as nothing, the scene accompanying his casual explanation reveals he tore out of his Quinque Steel body restraints and ripped a truck in half.
Kurogane is like this. Though he has an initially calm attitude when Seishiro "kills" Syaoran in Oto, you can just tell there's the hint of death in his dialogue and in his face. Though it's hard to tell if he's more mad about Syaoran's "death" or Fai's. Either way, don't mess with anybody in his party.
In the second sequel series Yu-Gi-Oh! 5D's, Crow goes on a Roaring Rampage of Revenge when he returns after the appearance of the Dark Signers' evil fog to find out the kids he's taken in have all vanished.
Also Jeager (to an extent). You may not be able to tell when you meet him, but he'll do anything for his son. (In one episode, when he and his family were down on his luck, he went hungry in order to feed his wife and son, telling them he'd "already eaten". Unfortunately, he's a Bad Liar.)
Napolean from Yu-Gi-Oh! GX is an interesting case. He wants to be his son Martin's protector, but he can't; as a teacher at Duel Academy, showing favoritism towards a student is a professional taboo, so he's forced to isolate himself from Martin (one of the hardest things he ever did, as he put it). As fate would have it, Martin becomes the victim of Demonic Possession, courtesy of Yubel, at which point Napolean pleads with Judai to help him.
Yusuke from YuYu Hakusho is a subtle example. Harming/killing at least one of his loved ones gets mad, but if it's Keiko or Kuwabara, he will kick their ass!
The best example comes from the battle against Suzaku, who was stronger than Yusuke, capable of creating six clones of himself (all strong as the original) and, once he clones himself, has to be killed alongside all his clones, because leaving just one barely alive will only lead to him absorb the rest, heal himself and summon six clones. Obviously, Yusuke was having a lot of trouble, but as soon as Suzaku threatened Keiko and Botan he killed six of the Suzakus (including the original) and grievously wounded the seventh. At that point Yusuke was exhausted, but the survivor had absorbed the others to heal and cloned himself again... At which point Yusuke used the power of his own soul (a move that nearly killed him) to recover the strength, and overpowered and killed all the Suzakus at once.