Played for Laughs in a current TV ad from Phillips 66 — a woman is sitting at her husband's bedside in a hospital, and between her sobs says that she never had a chance to tell him that he'd won free gasoline for life (a promotion run by that company). He immediately sits up, yanks his life support equipment off, announces that he has something to live for, and charges out of the hospital room.
Happens to Nico Robin in One Piece. Robin was on the verge of giving up on her life, and Luffy was the light at the end of the tunnel. Her time with the crew was the happiest she had ever been — and she cared for them so much that she willingly turned herself in in order to save their lives from the Buster Call. The Straw Hats come to rescue her from being executed, and refuse to abandon her just because she had the entire world as her enemy. Just to prove their point, they declared war on the entire world for her sake. It was only then that Robin realized that she had finally found her place.
When Luffy nearly passed the Despair Event Horizonover the death of Ace, he remembered that he still had his crew. It was only because of them and the fact that Ace would have wanted him to move on that Luffy bothers continuing to live anymore.
Ace had tons of angst over his bloodline, to the point that the question he spent his entire life searching the answer for... was whether he not he deserved to be born. Living only stopped being so painful when Luffy, and eventually, the Whitebeard Pirates, came into his life, having finally found the answer to that one question. All of it only serves to make his death more tragic.
In the X1999 anime, Kamui falls catatonic after Kotori's death, but Subaru manages to convince him that his life is still worth living, if only to save Kamui's best-friend-turned-evil (and Kotori's brother) Fuuma. Much later in the series, Kakyo and Subaru's ghostly sister do this for Subaru himself (who falls catatonic after killing Seishirou), just in time for him to save Kamui again.
Devilman: Awfully subverted. The Hero Akira Fudo merged with a demon to fight other demons and protect humankind. However he is finding Humans Are the Real Monsters and they are just as bad as demons. He is feeling his resolve to fight is wavering when he remembers he has something worth to fight for: Miki. He rushes towards her home only to see the place burning down. A mob had chopped Miki and her whole family up in pieces and had set their home on fire. Grief-stricken, he thought he had nothing left to protect... but he would keep fighting if only to stick it to Satan.
Mazinger Z: In one episode, secondary character Erika asks Kouji why he goes so far to fight Dr. Hell, no matter how much he suffers or how many times he gets hurt. Kouji tells her it hurt a lot when his grandfather got murdered by Dr. Hell, and he wants nobody else to go through that. And if Dr. Hell conquers the world, that is exactly what will happen to millions of people, who will lose their families and will be enslaved. It is because of them that he is fighting, not only for revenge.
Yaiba: One character asks the main character why he wants to keep fighting. Yaiba answers his dream is becoming the world's best samurai. When that character notes he will be fighting countless battles and asks what if he fails, Yaiba smilingly replies that he will look for another dream.
In Claymore, when Teresa is sentenced to be executed, she refuses because she has found something worth living for in Claire.
One of the major aesops in Monster. What would stop someone from being a monster and start being a human?
At the same time, the anime shows Homura is willing to sacrifice herself for Madoka's sake. And in Puella Magi Madoka Magica The Movie: Rebellion Homura decides that Madoka isn't just worth living and dying for - she's also worth becoming a monster for.
While it was his aim to survive in the first place, Guts from Berserk stopped wasting his life away for the purpose of revenge and stopped acting so sociopathic when he realized how the end of his life would ultimately mean the end of Casca, his ill-fated lover, as well. His current mission is trying to find a cure for her insanity.
Because of this, by Episode 24 of Gosick Victorique finally fears death.
Climax of Noir has Mireille holding onto Kirika via one arm over a Lava Pit. Kirika is pretty much content to die; especially since as a Tyke Bomb she had killed Mireille's parents; Mireille; crying; begs her to live. Kirika looks up; sees that Mireille is the one person who gives a damn about her; cries as well and lets Mireille pull her up.
In Y: The Last Man, Yorick Brown, the last man on Earth after a Gendercide, repeatedly throws himself into harm's way due to his overwhelming survivor's guilt, until a suicide intervention sets him straight. This gives him an epiphany, showing him the one thing he thinks is worth living for. At the end of the series we find out that it was his bodyguard, Agent 355.
In Watchmen, Doctor Manhattan spends most of the story in a state of detachment since his skewed perception of time makes him think that everything is set in stone no matter what he or anyone else does. The combination of a tachyon swarm disrupting his ability to see anything but the present and the revelation that Laurie is the Comedian's daughter trigger an epiphany. Doctor Manhattan ponders the multitude of coincidences that resulted in Laurie's existence, realizes that everyone alive is just as miraculous, and finally feels the urge to do, well, anything again.
As several characters in Touhou are explicitly or not-so-explicitly immortal, some Fan Fic writers explore the reason they keep pushing forward despite the obvious existential angst. This trope is commonly brought into the story for Mokou and Eirin, with Keine and Kaguya as their respective reason to live. Note that Keine isn't immortal despite having a very long lifespan; it takes Mokou serious courage to forge a bond with her.
In Igor, Scampers is an immortal rabbit with no will to live, and makes several humorous suicide attempts throughout the movie. Eventually he finds friends, which gives him the will to start living. However, this causes problems when he's on a Conveyor Belt of Doom towards a raging inferno and is concerned that this might actually kill him.
It's more fortunate for Igor and Brian that he wanted to live; otherwise, he might have just elected to go through with it.
Desert Heat: Eddie Lomax finds Rhonda to be his reason to live.
Gravity: The borderline depressive Dr. Stone realizes that life itself is worth living for, after finding herself desperately fighting for survival and Kowalski sacrificing his life for hers. Not only does she find the will to live again, but she also re-discovers the dignity and resilience to withstand and overcome the hardships life throws at her.
Happens in Brisingr after Eragon almost drains himself of life-force casting powerful spells. A bumblebee lands in front of his nose, where he can contemplate it in detail from a couple inches away, and he realizes that a world that can produce something so vibrantly alive as that bee is one he wants to live in.
In Those That Wake and its sequel, Laura and Mal are this to each other, as are Tommy and Annie.
Stephen Franklin, having been stabbed, and after being berated by a hallucination of himself giving him a potent "The Reason You Suck" Speechwhich turns into a sort of Rousing Speech, realizes that he wants to live, and is willing to fight to survive, even if it means making all of the same mistakes all over again.
After Sheridan's death at Z'Ha'Dum, he is challenged by Lorien to find something worth living for, rather than merely finding something worth dying for. For Sheridan, it turns out that the one thing in his life worth living for is Delenn. This helps him persevere towards the end of the fourth season after he is captured and subjected to Cold-Blooded Torture.
Before Lorien, this had been brought up by Garibaldi in the episode "Infection":
"I know a lot of guys who came out of the war changed. Some came out better; some came out worse. A lot of them had this problem. The war gave them definition, direction, purpose. Without it they don't know how to fit in anymore, so they keep looking for ways to go out in a blaze of glory. Some people call that being a hero, maybe so. I don't know. I've never been one. Me, I think they're looking for something worth dying for because it's easier than finding something worth living for."
Cain's arc in TinMan. He was dead-set on killing Zero to avenge his family, then dying. But then his former boss appeals to his honorable streak and forces him to promise that he'll guard DG the lost princess of Oz "at any cost." Cain is still Lawful Good enough to not turn down the Mystic Man's Last Request. Between this and learning his family survived, he's got enough Heroic Willpower to fend off a bullet and hypothermia.
Discussed at the end of "The Doctor's Daughter". The Doctor spends the episode coming to terms with the presence of Opposite-Sex Clone Jenny, only for her to be shot. She "regenerates" (sort of), but the main cast leave before it kicks in.
Martha: All those things you've been ready to die for... I thought, for a moment there, you'd found finally found something worth living for.
Doctor: Oh, there's always something worth living for, Martha.
Detective Inspector Thomas Lynley and Detective Sergeant Barbara Havers, for each other, on The Inspector Lynley Mysteries. At one particularly low point in Lynley's storyline, he shows up at Barbara's flat in the middle of the night and point-blank asks her how she manages to keep going, living all alone as she is. She gently tells him that you have to find something worth getting up for. There's a reason this is the show's Fan-Preferred Couple...
Lynley: How do you do it? Living alone.
Havers: Oh... you get used to it. I've never been married, never had anything you could call a relationship. So you get to a point where you just have to accept what you are, what you have. And then you find something else, and that gives you the reason to get up in the morning. And I have that, don't I.
Lynley: We both do.
Mystery Science Theater 3000: Red Zone Cuba. Doctor Forrester gets beaten into a pulp by a mob enforcer at the beginning of the episode. Later, he appears to die in his hospital bed, only to suddenly wake up and declare that he has too much to live for. He climbs out of his hospital bed, stumbles out of the room... and immediately gets beaten again by the same mob enforcer.
Solid Snake decides this in a long speech at the end of Metal Gear Solid after learning he has been infected with a disease that he thinks will suddenly stop his heart without warning. The difference is that instead of being a Death Seeker, Snake has focused entirely on survival rather than on enjoying life.
Then played touchingly straight at the end of Metal Gear Solid 4, where Snake knows his time is drawing near, but is now content to see it out peacefully in retirement. He even quits smoking, saying to Otacon "those things will kill ya."
Knights of the Old Republic: All Carth was living for was the chance to destroy Saul Karath and die in the process. But by the time Saul is killed by the party, he's come to find more than simple revenge to live for. Protecting the Player Character from themselves and the Dark Side has become his reason to keep going.
Throughout the series, it's been theorized that a lot of the vicious infighting and turmoil among the krogan is due to them not having any hope for the future, thanks to the genophage: without any hope for the next generation, there's no incentive for them to work together or... do anything but fight, drink, and make money, really. In Mass Effect 3, Wrex demands a cure for the genophage in exchange for krogan help with the war effort, hoping that it will re-inspire the krogan species.
The immortal Zasalamel in the Soul Series initially wanted to use Soul Calibur and Soul Edge to remove his immortality because he was weary of the endless and painful cycle of death and rebirth. During the ritual that would make him mortal again, Zasalamel saw a vision of humanity's future. He was so amazed by it that he interrupted the ritual, having regained the will to live.
In Tsukihime, Shiki lets himself be killed by vampire Yumizuka Satsuki due to his promise to her earlier in Akiha's route unless you answered earlier in a fashion that makes him realize he has to live for Akiha.
In Little Busters!, this is arguably the whole point of the game: that is, showing Riki and Rin that even if their friends all die, they can still pick themselves up and have a reason to keep on living. It's most obvious in Riki's arc, where he realises after the other Little Busters died that it was his parents' death originally that closed his heart up, but that because of the efforts of his friends and everything he and Rin had done together over the game he could now accept the bad things that had happened and understand that having been born itself was a wonderful enough reason to keep living.