When an anti-heroic or outright villainous character is forced by circumstances to work with a heroic character and over time, becomes more selfless and cooperative as a result (though not necessarily to HeelFace Turn levels). They may even blame The Hero for making them go "soft" often right after a Conscience Makes You Go Back or a Changed My Mind, Kid moment. This is even more likely to occur if the heroic character is a Messianic Archetype, an All-Loving Hero, etc.
A type of Character Development. Toxic Friend Influence and Peer Pressure Makes You Evil are the opposites. Compare Got Me Doing It (which is about mannerisms rather than internal values), Good Feels Good (which is about good's inherent superiority over evil, rather than personal influence), and The Paragon (who actively strives to make this happen). Compare/contrast Morality Pet, who induces niceness in a villain who otherwise remains perfectly vile.
- Kyouko in Puella Magi Madoka Magica is introduced as an Unscrupulous Hero and clashes violently with the heroic Sayaka at first. However, after the true nature of magical girls is revealed to them, Kyouko grows more attached to Sayaka, rediscovers her own long-forgotten heroic self, and ultimately commits a Heroic Sacrifice to stop a rampaging Witch!Sayaka.
- Luffy from One Piece is hardly a hero (and doesn't want to be one), but he has a massive problem with powerful people abusing their power and often demonstrates it with his fists. Thanks to his charismatic and caring nature, this attitude quickly takes hold on most of his crew mates, even on the stoic and previously uncaring swordsman Zoro.
- Zabuza from Naruto has a moment of this due to Haku.
- Both Piccolo and Vegeta from the Dragon Ball franchise fell prey to this, though it took a lot longer with Vegeta.
- Ymir in Attack on Titan starts off as an extremely cynical and egoistic individual, but falls in love with the (unhealthily) selfless Christa Renz, and undergoes much character development under her influence (as well as vice versa). Before she is Put on a Bus, we last see her sacrificing herself for Christa, as well as for Reiner and Berthold, and musing about how nice it feels to be a "goddess" for a change ("Goddess" being Christa's affectionate in-universe nickname among her comrades).
- Mittens the cat would've been content to stay behind in Las Vegas while Bolt continued to Los Angeles, had not Rhino reminded her of Bolt's selfless ethics. Bolt's heroism is infectious to the point that Mittens rescues Rhino the hamster during his Heroic Sacrifice, something that would have been inconceivable when Mittens and Rhino first met.
- Han Solo in the original Star Wars trilogy starts off as a smuggler pilot, who is quite a mercenary and only helps Luke and the Rebels for the cash they offer. Before long, however, he gradually becomes a heroic Rebel leader himself under the influence of the very heroic Skywalker siblings.
- The Naïve Newcomer Will and the Loveable Rogue Jack seem to have respectively a positive and negative influence on each other through the Pirates of the Caribbean movies. Jack becomes more selfless, not much, mind you, but he does improve a bit, while it's inverted with Will, who becomes more ruthless.
- In Labyrinth, Sarah does this with the dwarf Hoggle, gradually inducing him to be less selfish and cowardly, while undergoing a Coming of Age Character Arc herself.
- And in the Spiritual Successor MirrorMask, Helena does this with the scoundrel Valentine, while remaining steadfastly heroic herself. In this case, Valentine's growth is the main dramatic counterpoint of the film.
- Downplayed in Discworld. One of Carrot's defining traits is that he expects people around him to behave and be good to each other, and they do. The effect from his presence tends to be temporary, and wears off shortly after he's gone, but as long as he's around, it works on just about everyone.
- In the first two Artemis Fowl books, career criminal Mulch Diggums only works with the rest of the cast in exchange for time cut off his sentence or a Mercy Lead over the cops who want to arrest him, or as a result of being blackmailed. By the third book, he's incredibly annoyed to learn that he's developed a fondness towards Artemis and is prepared to commit an entirely non-selfish act to prevent Artemis being kidnapped by the Chicago mob.
- Doyle in Angel. In the first episode, he is reluctant to help Angel in any way other than getting the visions and passing on the message; after Angel forces him to come along to Russel's place, Doyle almost bails when he hears gun shots. Fast forward to the episode Hero, where Doyle decides to make a Heroic Sacrifice instead of Angel.
- Doctor Who:
- Jack Harkness; when he's introduced in "The Empty Child", he's a time-traveling scam artist, but his time spent travelling with the Doctor turns him into an Anti-Hero. He acknowledges the change in "The Parting of the Ways" when he's preparing to make a Last Stand against the Daleks to buy the Doctor some time, commenting good-naturedly that he wished he'd never met the Doctor because he preferred himself as a coward.
- "The Vampires of Venice": Rory Williams calls the Doctor out for this, pointing out that the Doctor is terribly dangerous because he inspires people to try and impress him. Ironically enough, Rory himself goes with Amy to assist the Doctor in saving Venice, the Doctor recalling Rory's words.
- Kamen Rider Build: It's actually lampshaded that Sento's ideals are infectious. His attitude will gnaw even on the true, hardcore cynics because he is the silly, idealistic rabbit. It kind of bugs him if people decide that the love and peace they fight for should include him too, though.
- Aside from "honest man" Nate Ford, the main cast of Leverage start the series as a misfit collection of unapologetic criminals who are mostly out for their own self-interest and were brought together by the promise of money. Realizing how much more effective they are as a team convinces them to do a second job together... but then Good Feels Good really starts setting in, prompting them to stick together for "one more." By the time the second season begins, they find that their old selfish ways no longer give them any satisfaction.
Eliot: This is the problem with being the good guy. It gets under your skin.
- PJ, your second Wingman in Ace Combat Zero: The Belkan War, is much more influenced by your behavior than Pixy, your original wingman. If you follow the Knight path, his dialogue will be all about protecting civilians and ending the battles quickly. On the other hand, if you fly as a Mercenary, he'll eventually be Only in It for the Money.
- This is a gameplay mechanic in Knights of the Old Republic II: not only are you able to swing between the Light and Dark Sides of the Force, but you can also build up Relationship Values of your party members to sway their own attitudes towards Light and Dark from their default positions to whatever philosophy your support, so the Light-Sided Exile will inevitably do this to her Dark-Sided companions.
- Mass Effect:
- Garrus is unique as a companion in Mass Effect in that you can shift his attitude to life with your actions and dialogue. He starts off as a frustrated Cowboy Cop, but traveling with a Paragon!Shepard convinces him that playing by-the-book is the better alternative. Of course, working with Renegade!Shepard only reinforces his original beliefs.
- In Mass Effect 2, you can continue to influence Garrus on his Loyalty Mission, but the game also gives us Jack, characterized as "the meanest and most spiteful creature in the galaxy". While she certainly tries to live up to that description, undertaking the Suicide Mission with Shepard brings out the more selfless traits in her. If she dies there, her Famous Last Words blame Shepard for her starting to "care". If she lives, she becomes a much more helpful and caring person by the next game, even jokingly blaming Shepard for bringing out her softer side.
- From the same game, there's also Miranda Lawson. At the beginning, she is one of the most loyal operatives that the Illusive Man has in all of Cerberus. At the end, she dramatically gives her resignation from Cerberus, having become even more loyal to Shepard.
- Isabela the Pirate Girl in Dragon Age II is introduced as a kind of woman who'd kill without a second thought, never commit to serious relationships, and run off with a precious artifact while you're not looking. However, with enough Friendship or Rivalry, she will ultimately return said artifact to the Qunari to prevent more bloodshed in Kirkwall—and blame Hawke for having a bad influence on her.
- Parodied in Sam & Fuzzy. The majority of the comic's early story arcs revolves around Sam being drawn into Mr Blank's plot to resurrect the defunct Ninja Mafia (and Mr Black's desire to keep it dead). One of the players in this plot ends up being Getrude Dupont, who spent most of her life training in the hopes of becoming Ninja Emperor, a position Sam basically stumbled into under false pretenses. When the position is in her grasp if she just lets Mr Blank kill Sam, she finds that she cant go through with it, and points out that, out of all the people she has betrayed and backstabbed in her life, Sam was the only person who ever expected her to do the right thing, and it makes her want to do...something.
Sam: Be a better person?
Gertrude: No, that's not it...
Sam: ...pretend to be a better person while you think I'm watching?
Getrude: That's the one!
- Green Arrow from Justice League was already a hero but is introduced adamantly refusing join because he doesn't like the League's style. They only seemed to fight the "big monsters" while he preferred help the "little guys". However, after he takes down a giant radioactive "monster", he starts to reconsider, that and Black Canary walking by didn't hurt either. Interestingly, it's later implied that he is playing this role for the rest of the League — that Green Arrow is acting as a kind of Morality Chain for the more powerful members of the League, keeping their attention on the "little guys".
- Star Wars Rebels: Ezra Bridger is originally a "street rat" who's mostly in it for himself. This changes when he joins the crew of the Ghost and sees how often they put themselves in danger to help others, inspiring him to do the same and setting him on the path to becoming a Jedi.