Ensemble Dark Horse extraordinaire and Hollywood Cyborg Jeremiah Gottwald of Code Geass fame has one scene when an EMP-like weapon is used to disable his mechanical parts (which comprise a significant part of his body), thereby rendering him immobile and powerless before Lelouch. A few seconds pass, however, and Gottwald continues to advance toward Lelouch by sheer will, apparently grating some meat and metal parts together and causing himself great pain. He doesn't stop, however.
This is the ability of one of the main characters in Claymore. She can go "past the point of no return" in accessing youma powers, but still come back. She can also use this ability on others.
Deconstructed when she fights Priscilla. The only way that Clare will have any chance of beating the latter is by fully awakening. However, her Heroic Willpower subconsciously prevents her from being able to unleash her maximum potential, resulting in an almost instant Curb-Stomp Battle that ends very badly for our intrepid heroine.
Jean has just as much willpower as Clare, if not more. This is evident in her introductory scene, where she manages to withstand being tortured for hours on end while her comrades succumb to the pain and Awaken. Miria lampshades this when she says that Jean's being able to return to normal after her body had fully Awakened "must be due to an extraordinary strength of spirit" (though Clare's intervention certainly came in handy).
Mahou Sensei Negima! has Jack Rakan rewrite reality on force of will alone. Once to break a trap dimension, and again after being deleted from existence.Twice! Breaking the trap dimension was eventually justified as taking advantage of some obscure magical theory no one has ever heard of. The other two received no handwave.
In Tokyo Mew Mew, Deep Blue has told a sobbing Mew Ichigo that her precious Aoyama-kun is no more. Out of nowhere, Masaya's spirit manifests, taking control of the body again, and begins a cycle of Heroic Sacrifice suicides and resurrections by True Love's Kiss. They eventually sorta cancel each other out, leaving them both alive.
Devilman is about a timid teenager with a pure heart who allows himself to be possessed by a powerful demon, so he can use that demon's power to fight and kill its comrades (thus, preventing an oncoming demonic invasion.) The boy's personality gets altered after merging with the demon, making him more aggressive.
One OVA involves him undergoing enough psychological stress he loses his Heroic Willpower and spends the finale battling inside of his own mind to regain control.
In Tengen Toppa Gurren Lagannmain love interest Nia fights against her newly discovered Anti-Spiral purpose and allows Simon save humanity from the enemy's Extermination System. Further, even though she's a “virtual life form”—essentially an interdimensional Projected Woman with No Ontological Inertia—she defies this and continues to stay by Simon's side for some time even after the Anti-Spirals were blown to smithereens, essentially existing moment-by-moment through sheer willpower.
The page for TTGL says this grows on trees in that world. Not Quite… It grows in everything with DNA. Though they call it Fighting Spirit/Spiral Power, and everything with a spiral to it has it or can be used to generate it. Yes, everything. Even That.
Subverted in Dragon Ball Z by the reformed Vegeta, who gets possessed by an evil wizard, then though sheer willpower refuses to obey the wizard's commands to kill a god... and then attacks Goku anyway, revealing he chose to be possessed in order to get the power needed to crush his old rival.
In the 3rd InuYashamovie, Swords of An Honorable Ruler, the titular half-demon gets possessed early on by the evil sword So'unga, which then orders him to slaughter a helpless mother and her child to stop the baby's wailing cries...to which he responds by sinking his teeth deep into his own arm to hold the sword at bay long enough to get everyone out of harm's way before it overtakes him and forcibly unleashes a Dragon Twister.
While more a display of Heroic Resolve than Willpower, Sesshoumaru of all people solves Inuyasha's problem later in the film by forcibly taking the Tessaiga, seething pain of the barrier around it be damned, and blasts So'unga with a Wind Scar.
Played straight for the most of the series with Luffy surviving a massive internal damage just with willpower or Portgas D Rouge delaying the Birth of Ace for 20 months to keep him save and accomplishing that with just willpower.
Subverted in the Impel Down arc of One Piece. Sure, Luffy has the heroic willpower to fight through anything. Which is why Magellan had to use a bajillion different poisons on him instead of just one, meaning no medical antidote would work. Double Subverted later, when Ivankov's treatment allows him to fight the poison directly with his will, and he wins (almost dying in the process).
In Yu-Gi-Oh!, Yugi stopping Yami from attacking Kaiba in the Duelist Kingdom arc may qualify.
Ryou Bakura fighting Yami Bakura from the inside during the Monster World storyarc in the manga certainly counts. Even after Yami Bakura takes control over his body, what's left of Ryou's consciousness manages to fight back and screw his dark counterpart up enough for Yami Yugi and friends to defeat him.
Jiraiya from Naruto, who literally brought himself back to life after his heart stopped beating for a while from being stabbed in the back with 6 piercing rods through willpower alone.
In 30 Days of Night, sheriff Eben Olemaun allows himself to be infected with vampire blood in order to become strong enough to defend his town. It works, and even though he's ravenous for human blood he manages to control his urges and fight and kill several vampires, including their leader. He doesn't turn human again afterwards though, and allows himself to die when the sun finally rises.
In Batman Hush, Superman is controlled by Poison Ivy's special Kryptonite blend of mind-control lipstick, leading to a big fight with Batman, who frantically stacks the deck by playing Superman's innate boy-scout tendencies against him—-those base-level urges are so innate to Superman that Poison Ivy couldn't make him ignore them. The control is finally broken by a supreme burst of Heroic Willpower caused by Catwoman shoving Lois Lane off of a building.
Midnighter gets a moment like this when he (along with Jack Hawksmoor, Jeroen, and most of the planet) is infected with an evil cult virus. Though the virus has made him obedient to the cult's will (so much so that they've got him flogging himself), he manages to hold out until Swift rescues him. Why? Well, the fact that they wanted him to publically break up with his husband Apollo and denounce his former lifestyle might have had something to do with it.
During the Marvel Zombies/Army of Darkness crossover, Doctor Doom reveals that he's been infected with The Virus. The reason he doesn't attack the heroes is because he's so incredibly Bad Ass that he's just holding it off because no goddamn virus is going to mouth off to Victor Von Muthafuckin' Doom.
Deadpool while temporarily infected by a T-O Virus (in a reality hopping storyline), complete with the obligatory Must speak like William Shatner?! line.
In the Spider-man comics there's the good symbioteToxin (the host is a cop, and new father who decides to use this powerto do good). Also the lesser known character Hybrid (though he/they are something of an inversion with the symbiote(s) being more placid and the human host more prone to Unstoppable Rage.)
The Green Lantern Corps is powered, quite literally, by heroic willpower.
Guy Gardner in particular has so much willpower that his ring can barely contain it, causing it to constantly spark with energy when it's not actively used. He's also one of the few beings who could control a Red Lantern Ring without being consumed with Unstoppable Rage.
Danny "Iron Fist" Rand can focus his chi so intensely that he can punch through steel and cure cancer. At the same time.
The Avengers' foe Grim Reaper thought it would be ironic to turn dead Avengers into zombies to use against the still-living ones... and then found out the hard way that Avengers fight evil even beyond death.
Not quite "Heroic" Willpower, but Doctor Doom gets one in the Emperor Doom arc, where he's used the Purple Man's powers to take over the world. The Purple Man tells Doom he couldn't have done any of this without his help, at which point Doom removes the mask that protects him from the Purple Man's powers and just stares him down while the Purple Man keeps giving him commands he doesn't obey. Now, Zebediah Killgrave... WHO deserves to rule?
Doctor Doom once went toe-to-toe with a Physical God called the Overmind, who professed to have the mental and physical strength of billions of aliens. He had already effortlessly mind-controlled Mr.Fantastic into trying to kill the rest of the FF, when Doom showed up. Doom simply IGNORED the mind-control, while simultaneously boasting, fighting, and being nearly killed... to save the man he hates more than anyone in the universe. And he did it all just to prove (to his arch-enemy's wife!) that he wasn't scared.
This is essentially one of Spider-Man's powers. In fact, on some battle forums, this mode is sometimes called "Aunt May Mode" or "Mary Jane Mode" because roughly once a year since his inceptation, Spidey has had one of these moments in which he utilized this trope, often when his loved ones were in trouble (or at least the moment was brought on when he thought of them). When this happens, he goes far beyond his normal limitations. Examples include:
Being trapped under a bridge when he needed to get to Aunt May, he actually lifted the entire bridge to free himself. The most impressive part of this scene is that this happened while he was a teenager, a time in which he was at his lowest power levels.
During one arc in the Giffen/DeMatteis run on Justice League of America, a street punk got his hands on Big Barda's Mega-Rod, her signature weapon. The Mega-Rod, forged on Apokalips, constantly sends out subliminal mind-control messages commanding that its wielder submit his/her will to Darkseid. By the end of the issue, the street punk was an emaciated slave living only to serve Darkseid. The fact that Barda is able to wield the Mega-Rod and can shrug off its mind-controlling properties speaks volumes of her levels of willpower.
In Post CrisisMartian Manhunter comics, it was established that the shapeshifting, telepathic Martian race was wiped out by a psychic plague that caused the victim to shapeshift into a form that would spontaneously combust. The only way to save oneself was to avoid telepathic contact with anyone, an almost impossible feat for a race that maintained low-level esper contact constantly. J'onn survived because he was able to hold out the longest without telepathic contact, tragically leaving him as the last man standing. J'onn survived because he was literally the strongest-willed person on his whole world.
In The Lost Boys, the older brother, Mike, is given blood that's slowly making him a vampire. After a climactic battle where he, his brother and friends defend their home from the vampire gang that was turning him, he manages to beat the strongest vampire in the gang. When he doesn't turn human again [[spoiler: and the real vampire lord show up, he beats him too and finally regains his humanity.
Doom (the film) revolves around a chromosome which, when injected to people with an "evil" gene, turns them into murderous monsters. When Reaper is injected with it, he becomes superhuman, since he doesn't have the evil gene.
And also, one of the marines realizes that he is infected and brains himself to death before he can turn.
Sufficient fridge logic can lead you to the conclusion "If the main character is good because he regrets his alluded to arguably evil acts, and thus turns superhuman... shouldn't the man who realized that he could kill everyone by turning and sacrificed himself to save his friends be just as good?"
...no. Remember, it was the "evil gene" that caused them to turn into monsters instead of superhumans. Grim's sister thinks that its the same gene that makes people evil, but she could be wrong. All we know for certain is that Goat had this gene (as did most of the other mercenaries), and Grim didn't.
This is also implied to be how only some people escaped demonic possession in Doom III.
Evil Dead II had our hero Ashley Williams corrupted and turned into a Deadite. He couldn't actually fight it off when it mattered, beating the hell out of the only other survivor and approaching her unconscious body to finish her off. Then he came across the bit of jewelry that he'd given his girlfriend earlier in the film, lets out a howl of pain, and successfully fights off possession.
Serenity: despite River Tam's brain is explicitly stated to be surgically altered to remove her ability to control her own behaviour, she nevertheless becomes less insane and more stable in the end of the film, with no explanation other than Heroic Willpower and the Power of Friendship.
Getting the secret of Miranda off her chest seems to have helped too.
Skyline: while everyone else who gets their brains put into alien bodies seems to lose all personality and will, the male lead uses his powerful new body to kick alien butt when they endanger his pregnant girlfriend.
Puma Man: all of the good guys except the so-called "hero" manage at one point or another to resist the effects of the ancient mind control mask.
In Terry Pratchett's Carpe Jugulum, Granny Weatherwax pulls this one off with vampiric infection. An interesting twist is that she uses the blood connection to make the vampires weaker, rendering them unable to drink blood or harm humans and giving them an unnatural addiction to tea and cookies.
Then there's Sam Vimes in Thud!, as discussed in the "Quotes" section.
Vimes is freakin' made of this trope. It happened to him in Men at Arms, and got Lampshaded too: "The pounding spirit of the gonne flowing up Vimes' arms met the armies of sheer stoneheaded Vimesness surging the other way."
In The Tommyknockers, by Stephen King, Bobbi Anderson's sister Anne is a lifelong bully and control freak who makes everybody around her frightened and/or miserable. She has "heroic willpower" in exactly the sense Hitler claimed to have "fanatical will power." But when she is turned into a living battery for the Havenites, her ultradominant personality at least enables her to rebel and subvert the machinery.
Occurs in Good Omens: Adam is a 11-year-old boy who also happens to be the Antichrist destined to end the world. As the Apocalypse draws closer, he gradually becomes less like his playful kid self and more like a ruthless Creepy ChildReality Warper. When his friends make him realize that he's Not Himself, he visibly struggles against another presence within himself (presumably some hellish influence) and manages to regain control of himself to enact a Screw Destiny mission.
Edward Cullen in Twilight is a poster boy for this. Even though Bella is his singer, the one human whose blood is absolutely irresistible to him, he painfully prevents himself from killing her, since he "doesn't want to be a monster" and because he eventually falls in love with her. Of course, his blood lust is a metaphor for real lust, which he's also experiencing, and which he also has to demonstrate incredible willpower to resist, since he's sure sex would kill Bella.
All this in spite that Bella is more than willing to take a chance at the risk and its not shy of trying every waking moment.
Not only that. He manages to control his thirst so good that he can kiss her, hold her and eventually have sex with her without drinking her blood or killing her.
Bella herself also demonstrates this trope when she becomes a vampire, even being able to resist going after human blood when she catches their scent during a hunt and generally being able to control her newfound vampire senses and urges immediately instead of being blood-crazed for the first year as she was warned she would be.
Dragonlance has some not-quite-but-close examples. Raistlin who whilst opening the portal to the Abyss realizes he has failed just like his predecessor before him and was about to die and cause great destruction all around him as the portal was closing, through sheer force of will alone held the portal open long enough to enter it. The difference here is that Raistlin was not a hero, so it was more like Villainous Willpower, if there is such a thing.
His nephews Palin and Steel managed through will to brave their way through the Shoikan Grove — a passage that no mortal had ever passed before without an invitation from the master of the Tower.
Mr. and Mrs. Chapman in Animorphs #2, for a little bit.
In Invincible, Admiral Wedge Antilles can apparently prevent Jacen Solo from reading his mind through sheer determination.
In Parrish Plessis, Parrish's heroic willpower makes her the only one able to resist the influence of The Corruption after being infected. But even she succumbs to it in the end.
Necroscope's Harry Keogh contains his vampirism until he feels he can do so no more and then leaves Earth. Unfortunately he continues to try to do so when among his own kind, which ends very badly for him and everyone he cares about.
Harry Potter regularly fights off various threats that attempt to weaken or control his mind, such as the despair-inducing power of the dementors, although he is overcome by these the first few times. He also seems to be nearly immune to the Imperius Curse, a strength no other character shows, and in one case fought off bodily possession by Voldemort himself. His resistance is explained as a combination of this trope and The Power of Love.
It's also Subverted by the werewolf Remus Lupin, as (without the Wolfsbane potion) he cannot keep his mind when transformed, and attacks his own friends.
In MockingjayPeeta Mellark gets hijacked and brainwashed into wanting to kill Katniss, believing she's a mutt who's out to kill him. The main characters are told that there's no cure for hijacking and that nobody has ever recovered from it. In the end Peeta recovers almost entirely through sheer force of will.
In the later (in internal chronology) Dune sequels, gholas (clones) can be "awakened" (recover the memories of their previous life/lives) by programming them to do something their true self finds abhorrent to invoke this trope.
Live Action TV
Zhaan in Farscape had a variation of this happen to her. Tahleen, an evil member of her race, telepathically tore from her mind the knowledge she used to overcome a wasting insanity she suffered by telepathically murdering her former lover for being a traitor. The result was that she became borderline-sociopathic with red eyes. She managed to Snap Back thanks to sharing minds with Crichton, showing her that the kindness she was capable of was inherent and couldn't just be ripped out. As a result, she also became more spiritually powerful, and destroyed the evil priestesses' chance to grow stronger.
In the short-lived show Odyssey Five, Chuck Taggart is infected with Nanomachines that are slowly turning him into a "Synthetic", or cyborg servant to an Evil AI. As the process is about to complete and he links with the AI, he resists becoming it's servant and instead steals the knowledge needed to reprogram the nanites to turn him human again.
In the Doctor Who episode "Doomsday", Torchwood leader Yvonne, who helped cause an invasion of Cybermen by interfering with the Doctor, is captured by the Cybermen and undergoes Cyber-conversion. She manages to maintain her free will through her love of “Queen and Country” (or the fact that she was already robotic enough that the Cyberman procedure had no effect,) and holds off several of the Cybermen, at the cost of what was left of her own life, while the Doctor saves the day.
Subverted in "The Pandorica Opens". Auton Rory has enough Heroic Willpower to hold onto his identity and memories, but not enough to keep him from shooting Amy.
In "The Five Doctors", the Doctors combine their willpower to free themselves from being People Puppets.
In one episode of Knight Rider, Michael gets poisoned and becomes steadily weaker as he searches for the antidote. Towards the end, as KITT monitors Michael's vitals, he actually says “You're now operating on sheer willpower!”
Inverted in Stargate Atlantis, where the Wraith Michael manages to overcome the effects of a virus that turns Wraiths into submissive humans (on two separate occasions) through a sort of “Villainous Willpower.”
James T. Kirk is able to resist all manner of odds and temptations through sheer willpower and pure awesomeness in just about every other episode.
In the episode "Operation: Annihilate!", Spock is infected with a Puppeteer Parasite that causes violent madness through excruciating pain. Spock overcomes it through sheer force of will and is able to operate almost normally, with flashes of discomfort, until cured.
Henry Foss in Sanctuary learns to control his werewolf side and keep it from taking over in "Edward" (and uses his newfound skills to solve the Mystery of the Week). Later, in "Revelations" he resists the Cabal's attempts to permanently turn him into a werewolf and later turns just enough to escape from a cell without going all the way.
Shown by John in "Devil's Trap" when he is able to resist and trap the possessing Azazel for a moment. Later, he refuses to torture in hell to escape torture for one hundred years.
For thirty years, Dean resisted Alastair's offer to escape torture in Hell by torturing other souls. In "The Magnificent Seven", he resists Lust's charms.
Displayed by a demon-possessed Bobby in "Sympathy for the Devil" when he breaks the demon's hold just before it can kill Dean, and instead, stabs himself with Ruby's "kill-all" knife.
Sam in season five finale Swan Song took control of his body while the devil was riding it just so he could throw himself and the devil into hell's solitary confinement. In the season six finale, he drags himself to assist Dean and Bobby in the battle against Castiel and Crowley despite obviously suffering under the strain of his "hell memories".
Stefan Salvatore from The Vampire Diaries has struggled intensely for over a century with his blood addiction and blood lust. However, Stefan has managed to fight his urge to kill and drink copious amounts of human blood due to his strong morals. Because of this, Stefan has gone out of his way to not feed on innocent humans, however, he has not always been successful over the course of his immortal life. Due to his severe blood addiction, Stefan has succumbed to his weakness of blood addiction and has gone on a human blood and feeding rampage on and off over the course of his immortal life. When off the rails in terms of his blood addiction and bloodlust, he is known as the "Ripper" during this phase. However, due to his strong willpower, he has managed to pull himself out of his Ripper phase and control his blood lust as much as possible.
Inverted in Warhammer and Warhammer 40000, where Villainous Willpower determines which of the two possible Eldritch Abomination routes a follower of Chaos goes down - becoming a mindless Chaos Spawn or a Daemon Prince who retains sentience and control over his powers.
The Iron Will feat in Dungeons & Dragons gives you a bonus to resisting mind control, fear, and other mind-affecting magics.
Dungeons & Dragons 3.5 had Iron Heart Surge, which, due to poor clarification, can end anything from raving insanity to being pregnant, but due to manuver rules, can't break out of being magically held in place or Mind Control that Heroic Willpower typically ends (You need to be able to move to use a maneuver).
This is represented in White Wolf's Storyteller/Storytelling systems by the appropriately-named Willpower score, which aids in throwing off mental influence and enhancing various dice rolls.
In Exalted, every character also has a handful of virtues. Compassion, Conviction, Temperance and Valor are ranked 1-5 based on how your character views them and acts on them. If you're trying to do something that fits a virtue, you can use Willpower to boost to your roll. So if you're some sod beating his wife or a kid, and a Compassion 5 Exalt sees you doing it odds are you're about ready to get the beatdown of a century. (The flip side to this is that characters with high virtues have bigger issues with Limit Breaks.)
Hunters in Hunter The Vigil are able to do all kinds of impressive things with Willpower points. It's not quite on par with its use in Exalted, but that's because Hunters are basically limited to Badass Normal with a few extra tricks.
Willpower functions in a similar way in the other World Of Darkness gamelines. For example, not only is the difficulty of a Vampire's Dominate Discipline determined by the victim's Willpower (meaning that a character with maximum Willpower requires all but a perfect roll to control sucessfully), but certain merits, such as Code of Honor, or certain abilities, such as a Mage's Mind Sphere, can help increase the difficulty further. Willpower also determines whether or not a character falls victims to phobias.
The fuel behind superpowers in Wild Talents. Bottom out and your powers start to falter. Build it back up by conquering your foes, overcoming your inner demons, and being awesome.
Tales Of Symphonia's Applied Phlebotinum has the nasty side affect of turning people into monsters if they're not correctly protected. Marble sacrifices herself by exploding (!) into the resident bad guy. However, Lloyd and Genis had just beat the shit out of her after she attacked them, so maybe it doesn't count.
Happens to The Hero in Tales Of Hearts. The possessor ends up stabbing his host body and leaving. Shing gets better.
Ghost Trick: Lynne doesn't have enough willpower to completely fight off Yomiel's control, but she does make his first shot miss—which is what winds up killing Sissel, who was inside the box Yomiel was carrying.
The entire story of Neverwinter Nights 2: Mask of the Betrayer revolves around this, especially for good characters
In Grandia II, Ryudo gets a piece of the devil stuck in him. Through an extended dream sequence, he fights off the devil and comes out of the coma. Later when he tries to become a god (being the only person qualified in the room with a piece of the devil in him) he becomes a monster; later, through the power of song and friendship, he pulls through and becomes human again.
This is, in fact, simply a continuation of a recurring theme in the prequel series. Most notably, in Battle Networks 5 and 6. In 5, he is poisones by Dark Chips and can learn to use them more effectively. In 6, he gets posessed by a Cybeast (based on your version), and uses the Cybeast power to boost his own. It's reasonable to assume that the Cybeast instance is the inspiration for the OOPart posessing Geo in Star Force 2, by seeing all the similarities between the two.
Sergeant Nathan Hale in Resistance: Fall Of Man is an example of this trope, as even when he is infected with the Chimera Virus, he just turns into a lean mean bug-busting machine.
In World of Warcraft, undead player characters have a racial ability called Will of the Forsaken, which allows the player to escape from fear or mind-control effects.
In fact, the Forsaken are all this trope. They've all got The Virus, but they keep themselves free of the Lich King's normal dominance over the Scourge. The Lich King was weakened at the time, of course, but its still impressive.
The final raid of Cataclysm, we have the boss Ultraxion. His first move is to drag everyone into a shadow dimension, which players must use the temporary ability 'Heroic Will' to break out of at specific times to avoid death.
Your own character ostensibly manages this in the Baldur's Gate series, particularly if you play as a Good aligned character. You are the son/daughter of the deceased God of Murder, with wanton killing of innocents supposedly in your very blood, but through a series of dreams you fight off that influence and “remake yourself in your own image.”
More like Villainous Willpower, but Darth Sion must have a ungodly amount of willpower not to go batshit insane of his constant pain.
Revealed to be very important to a certain werehog in Sonic Unleashed. Sonic apparently has so much of this trope that he can practically guzzle down the power of an Eldritch Abomination yet be almost completely unaffected mentally. What's even more impressive is that he wasn't even aware that he was doing it.
Makes you wonder how he would act if he had learned that just before the final boss, Eggman had shot down Tails' Biplane, and subsequently flipped his shit.
Also, in Shadow the Hedgehog, when Shadow proves himself immune to Black Doom's control. Also slightly earlier when he recovered from his Heroic BSOD.
Also used in the Sonic Storybook Series entry Sonic and the Black Knight as this was one reason how Sonic was able to summon Excalibur and become Excalibur Sonic!
Subverted in Sonic Rivals 2; In the last mission of the stories of Sonic/Tails and Knuckles/Rouge, Ifrit, the monster of the game, will possess the partner to attack you throughout the boss. It has the same full effectiveness on all of them - even Sonic, the main hero. Of course, it's only very temporary.
In Mass Effect 1, Fai Dan is the only member of Zhu's Hope who is able to fully resist the Thorian's mind control. In fact, once the Thorian starts to successfully turn him in an attempt to kill Shepard, he uses the last of his free will to kill himself rather than be a slave.
Villain examples: The first game's both baddies, Benezia and Saren are also subjected to this. Benezia is able to resist Sovereign's mind control for a short time during her confrontation to inform, that they don't do this from their free will. Saren can be talked to Heel Realization in the beginning of the final fight where he will become lucid for a moment and shoot himself before falling again so that the Sovereign won't be able to complete it's plan through him, thanking Shepard with his last words
Subverted hilariously in Mass Effect 2, when Morinth suggests that since Shepard has the willpower to resist her attempts to enthrall them, they may have the willpower to resist her mind-frying Death by Sex. Turns out Sheparddoesnot!
Liara speculates that this was how Shepard was capable of withstanding the effects of the Prothean Beacon in the first game, which on a Weak Willed individual would most likely have destroyed their mind entirely. During their mind-melds, the sheer volume of information being depicted by the vision actually leaves Liara visibly exhausted after each attempt, while Shepard actually appears to become more resistant to it's effects.
The protagonist of Traffic Department 2192 demonstrates a partial example, albeit not in the way she intends. The villains attempt to erase her memories to make it easier to Brainwash her. To fight it, she focuses on the strongest memory she has—her father's murder—and keeps her mind on it even as it slowly degrades. It's completely erased, but by the strength of her will all her other memories are left intact.
IsaacClarke. Not only does he walk through dimly lit corridors full of freakish space zombies, he does it with an Artifact of Doom chipping away at his sanity. Granted, he isn't entirely unaffected by it, but he's able to persevere despite this. In Dead Space 2, he's far more in control of himself than Stross, another man exposed to the Marker's form of Mind Screw.
Bill of the Left 4 Dead mythos, in the starting wave of the infection, is being put under for surgery on his knee which had been damaged during his tour of duty in Vietnam. The nurse prepping him for surgery turns in the middle of it and attacks him. He forces himself to stay conscious through modern anesthetics, fends off the now turned nurse, and runs down the hall on said knee that required surgery to find himself a weapon. For reference, the reason said knee needed surgery is that it still hadn't and probably never would fully recover from being torn up by shrapnel during his tour in 'Nam. And Bill would go on to fight Tanks on it anyway.
Batman Arkham City both Batman and the Joker are infected with a poison (Joker poisoned a few people in gotham too, just for good measure) and are both dying. Even as it ravages his body, Batman fights on, doing what he has to to get the cure.
Batman: ...Oracle, how long have I got?
Oracle: Oh, thank God. I'm not going to sugar coat it. At this rate... I'd say minutes. What do you want me to do? If you don't-
Batman: I'll make it.
City of Heroes has this as an actual defensive powerset for Melee classes, mostly to reflect a more "natural" superhero who doesn't rely on fire, ice, rocks, energy or anything weird like that for protection. Most other sets hand-wave your ability to avoid damage as your armor deflecting or absorbing the damage. Willpower has you fighting on DESPITE taking grenades, energy blasts, super-powered fists and all manner of weaponry to the face. Incidentally, it is one of the best performing powersets in the game.
In Kingdom Hearts, after Sora stabs himself with the dark Keyblade and turns into a Heartless to save Kairi, all hope seems lost for his companions, as Ansem is likely going to kick their asses and kill them anyway... until Riku's spirit leaps out of Ansem's body, holding him off for just long enough that Kairi and the others can escape to Traverse Town.
In Disgaea 4, Valvatorez is the only character not to be infected with the A-virus. He attributes this to his strength of will and sardines.
Mötley Crüe Guitarist Mick Mars has struggled with a condition called ankylosing spondylitis for most of his life. This disease is a form of arthritis that causes the ligaments in the lower spine to fuse with the bone. His condition got so bad that when the band split up, he reportedly gave up guitar playing. However, when the band reformed in December 2004 (coincidentally this was after he had hip replacement surgery) he decided to take up playing again, saying that "he'll be damned if it (the disease) was gonna have his soul too". He is still one of the greatest guitar players out there.