Restored My Faith in Humanity

Bob long ago learned the painful lesson that Humans Are Bastards. They kill each other over the most trivial of reasons and treat anyone who is different as an outcast. And so Bob has given up on them, perhaps to the point of becoming the villain or even the Big Bad.

And then along comes Alice, a shining example of why humans aren't that bad after all. She'll listen to Bob's rhetoric about how humans are unworthy to live, smile, and retort with an impassioned speech about everything good about humanity or she'll just show him how wrong he is through her actions.

Bob will come to see that maybe he was wrong about humanity all along (it's very rare for Bob to accept simply that Alice in particular isn't so bad, or, if he does, he's missing the whole point), perhaps performing a Heel Face Turn or sacrificing himself to save humanity.

See The Messiah and Purity Sue for two character types Alice is likely to fall under.

Anime and Manga

 * in Tokyo Mew Mew acts like the nicest person on the planet
 * In Gankutsuou, when it seems to Albert that everyone is lying and good people are helpless to do anything, a letter from  Franz restores his faith in humanity, and he in turn.

Comic Books

 * Doctor Manhattan in Watchmen, though for him it's Humans Are Boring, not Humans Are Bastards.
 * Ironically, he comes to the conclusion that humans are too damn interesting in the end.
 * The High Evolutionary's plans to wipe out humanity were once waylaid by the Hulk's determination to survive in spite of everything.
 * In Grimm Fairy Tales, the Wicked Witch Belinda shows her friend Sela around a beach and explains that Humans Are Bastards by pointing out Jerk Jocks who bully others, a shallow girl who Really Gets Around, etc. When a building collapses, everyone Belinda pointed out immediately rushes over to help. The jocks use their strength to clear rubble and pull people to safety, and the shallow girl turns out to be a highly qualified doctor. Belinda gets disgusted and leaves, but Sela is amazed and is so touched that she decides to help too.

Film

 * In The Fifth Element, Leeloo loses her motivation to save humankind after witnessing its in-fighting and learning about its war-ridden past. However, Korben manages to restore her faith in humanity with The Power of Love.
 * Klaatu in both versions of The Day the Earth Stood Still is convinced that humans are worth saving, although in different ways.
 * Charlie and the Chocolate Factory: So shines a good deed in a weary world...

Literature

 * Jean Valjean, in Les Misérables, after being put in prison for almost twenty years for a minor infraction, is wandering the streets of a small town looking for somewhere to spend the night after a day in which nobody will pay him full wages or rent a room to him because he is a convict. Nobody will let him even stay on their stoop, but one person points out the door of the local bishop. He is given pride of place at the bishop's table, a room for the night, and respect as a fellow human being. However, this trope doesn't take effect until he steals the bishop's silver and makes a run for it, and instead of denouncing him to the police, the bishop actually gives him the rest of the silver as a gift. Cue Heel Realization, My God, What Have I Done?, and redemption. Valjean goes on to become one of the most benevolent and just characters in fiction.
 * Bartimaeus, the demon of The Bartimaeus Trilogy is given faith in humanity when he meets Ptolemy, the only human who ever treats him with respect, turning him into both The Woobie and a Noble Demon.

Live Action TV

 * Brutally inverted and then subverted in House. House has a deep faith in the negative attributes of humanity. His favorite phrases are "everybody lies" and "people don't change." Cameron, and later Thirteen, try to prove him wrong whenever possible. However, just about every patient House has lied to him and usually also the patient's family.
 * The Doctor is an...interesting case. He'll occasionally go on a very vehement Humans Are Bastards phase, calling them violent, selfish and stupid, and then, something will happen (usually sparked by his companion) that restores his faith in them. After all, there's got to be a reason he hangs out on Earth so much.

Newspaper Comics

 * One Bloom County strip had Opus wallowing in gloom, thinking he's lost the Christmas spirit forever. Portney appears and gives him a gift which turns out to be plastic dog-vomit. Opus hugs him, saying in total sincerity: "Thank you. You've pulled me back from the brink. I'll cherish it forever." Cue Portney wallowing in gloom.

Video Games
""Amazing! You've restored my faith in mankind! Actually, no, I still hate mankind. But at least you're okay.""
 * Gotoh in Fire Emblem 1, 3 and 11. The third game is the only one to directly explain why he didn't like humanity in the first place. He gave them magic, and they used magic for war.
 * Word of God for the 10th game notes that Nolan (who suffers from the 10th games lack of character expansion) has this as part of his backstory.
 * Ike can restore Sephiran's faith in humanity as well, though the requirements for it are a bit... obscure.
 * Ideon does this in the Normal and Good endings of Super Robot Wars Alpha 3, deeming that humanity has a possible future after talking it over with the loli manifestation of a powerful goddess.
 * In Mega Man Battle Network 4, Duo is a sentient asteroid that intends to wipe out earth because its people are wicked (Yes, he is attempting to commit genocide and we are the wicked ones. There is a reason people don't like 4.). after his fight with Megaman EXE, Duo seems to rethink it.
 * The World Ends With You:
 * Tales of Symphonia: Dawn of the New World:
 * In the Sam and Max episode Reality 2.0,
 * Mocked, naturally, in No More Heroes: Desperate Struggle when you complete the "Stings So Good" minigame.


 * in Skies of Arcadia.
 * In the Tokimeki Memorial series, this is the storylines of Kaori Yae (in 2) and Taku Komori (in Girl's Side 2) in a nutshell. Thanks to their relationship with their respective games' protagonist, they get to realize that there are trustworthy people out there, and as a result they gradually open themselves to others. Takafumi Wakaouji in GS2 also claims in his ending that the heroine has restored his faith in humanity, although this seems to be a bit of an exaggeration.
 * In Shin Megami Tensei: Strange Journey, has received the power of supernatural insight, or "brilliance," from the Schwarzwelt. Upon.
 * In Shin Megami Tensei Nocturne's "Resurrection" Ending,.

Western Animation

 * In Justice League, the Martian Manhunter flies off to what he thought was a secluded area on Earth, since after a telepathic sweep of the city, leaves him (accidentally) accessible to the petty, and selfish thoughts of humanity. However, he soon notices a search party looking for a girl that has gone missing, and hearing their thoughts, as well as the lost girl, learning that humans are decent after all, after finding her returning her back to the camp. He goes another one of this of sorts, in Justice League Unlimited when Wonder Woman notices he doesn't like humans and is "cooped up" in the Watchtower. She then insists he take part in the team's mission, before announcing he's taking leave and descends on Earth to live among humans. When he returns for the Grand Finale, it's later revealed that he not only was capable of living with humans, but he was in a relationship with one.
 * In Gargoyles, human ally Elisa Masa helps to restore Goliath and the Manhattan Clan's faith and trust in humanity after they had been betrayed by humans who destroyed their home and their people.