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troperville

Bob, possibly a Fallen Hero or Atoner, refuses to fight any longer. He decides he would rather become an Actual Pacifist or Technical Pacifist, or retreat from the world all together.

The reasons for this vary. Perhaps Bob now has (or gave someone) a dead little sister, or maybe they just think their quest has come to an end (though their opponents probably would beg to differ.) They may have simply met the one person who could convince him that murder is not always the answer. It could be a simple case of being beaten so badly and so often that they just give up completely.

Frequently, this becomes a 10-Minute Retirement, and Bob's once again forced to draw his sword and kill again.

When they don't give up long past where it's insane to continue, that's I Will Fight Some More Forever.

Examples:

Anime and Manga

Afro Samurai in "Resurrection". After finishing his quest in the first movie, he is no longer the killer he once was, turning to carving statues of all those he killed. Unfortunately for him, the new Big Bad still has a bone to pick.
Kenshin Himura from Rurouni Kenshin, after he accidentally killed his wife Tomoe.
- Though in his case, he swore off killing, not fighting or even swordsmanship. He got himself a custom-made reverse-blade katana so that he could use his sword to rescue people from their oppressors and attackers, but never again kill.
Train from Black Cat, after he met Saya and got tired of being Chronos' cat (i.e., servant).
Mewtwo from Pok�mon, after the events of Pok�mon: The First Movie.
Shinji in Neon Genesis Evangelion. Three times.
At the end of the Cell arc, Vegeta from Dragon Ball has the Antagonist In Mourning version. With Goku dead and no chance of ever settling their score, Vegeta is so crushed he flies away vowing to never fight again. Until the story skips seven years later when Goku returns for one day.
In Gundam Wing's Grand Finale Endless Waltz, the last line Heero Yuy says:
"I've killed Mariemaia. I will never kill anyone ever again. I don't have to kill any more."
(You know what was the most interesting part of that scene? *click* Empty chamber. He'd already killed his last person.)
Thorfinn goes from a Roaring Rampage of Revenge in the Prolonged Prologue of Vinland Saga, to this in the Farmland Saga arc.

Comic Book

The New Gods story "The Pact" has a pretty awesome example. Izaya, the leader of the New Gods of New Genesis, renounces the ways of war after figuring out that the entire war was Darkseid's gambit to remove the obstacles in his rise to power.
Izaya: I tear off my armor!! I reject this war-staff as a weapon!! I reject the way of war!! Darkseid's game is not mine! Where is Izaya!!!? Where is Izaya!!? IZAAYAA!
In IDW's Transformers #125, Optimus Prime gives up the Matrix and the responsibilities of being the leader of an army so he can be Orion Pax again.
- The Transformers: Headmasters #1 has Fortress Maximus, one of the Autobots' most powerful warriors and leaders, is sick of the war and resigns from the fighting to try find a new, quiet planet to settle where he won't have to fight at all.
Fortress Maximus: Whether I am a hero or a coward is not the issue! I am weary! My joints creak from the corrosion of war without end! I... cannot break this ring of hate that surrounds us all — but I can remove myself from it. No matter what you decide... I am leaving.
In Marvel's Age Of Apocalypse, the Juggernaut has become a pacifist monk and stands watch at the hidden sanctuary Avalon. When the sanctuary is attacked, Nightcrawler loses his shit at Brother Cain for refusing to fight back as people die around him. The desire to kill surfaces in Brother Cain and clashes with his desire for peace, and he winds up having an aneurysm.

Film

Jules from Pulp Fiction- The end of the movie (and if you listen closely, the beginning) has him wanting to retire from killing and walk the earth, and in fact, refusing to kill "Honey-Bunny" and "Pumpkin" who just held up the diner he's in, though that would have been the easier option.
Death himself from Death Takes a Holiday. He falls in love and gets preoccupied no longer wants to perform his duties.
The knife-wielding guy in The Guns of Navarone. It ends badly for him.
Rambo in the self-titled film qualifies for this... at the beginning anyway!
Hot Shots Part Deux
- Before the movie starts Topper Harley has resigned from the military and joined a monastery. Where he engages in martial arts contests. Okaaaay...
- Harbinger gives up killing, but Topper Harley teaches him the joy of slaughter once again. 10-Minute Retirement again.
Roy Batty the killer robot in Blade Runner elects to give a Tannh�user Gate speech instead.
In Danny the Dog, Danny chooses not to kill his opponent, and yells "No more killing!" to the man holding the forced gladatorial combat, who replies "I'm the only one that calls "'no more killing.'"
Quirt Evans (John Wayne) tells the marshal (Harry Carey) that he is no longer a gunslinger, but a farmer, in Angel and the Badman.
Notorious gunslinger/town marshal Clay Blaisedell (Henry Fonda) tosses his two gold-handled revolvers in the dirt before riding out of town in Warlock.
At the end of The Outlaw Josey Wales, Wales and his nemesis look one another in the eye, and agree to accept that the war is finally over.
BA has a 10-Minute Retirement of this sort in the A-Team Movie.

Literature

Subverted by Rudyard Kipling in The Second Jungle Book. In "The King's Ankus" Mowgli refuses to kill a treacherous cobra, claiming that he will never kill again save for food. Soon afterward in "Red Dog" the dogs of the title threaten Mowgli's wolfpack and he has no choice but to fight to defend it.
In The Night Angel Trilogy, Kylar the assassin tries to retire at the start of the second book - motivated in good part by his love interest not liking what he does. Both the goodies and the baddies are fairly insistent that he can't just walk away, though, and he does indeed return (although not by any means happily). His love interest eventually decides that it is indeed something that he has to do.
In Moses Man Of The Mountain, Moses, a military genius in his youth, vows to never fight again after murdering an Egyptian overseer and fleeing Egypt.
In The Children Of Hurin, Turin promises his wife Niniel he will never fight again unless it is in defense of their home, after spending his entire life looking for a fight. Unfortunately, You Can't Fight Fate.
In Warrior Cats, Mudfur loses his taste for battle and decides to become a medicine cat after his mate and all but one of his kits die the day they are born. He announces it after representing RiverClan in a Combat by Champion fight (and winning).

Live-Action Television

Possible Trope Namer, "I Will Fight No More Forever" is a 1975 made-for-television movie starring Ned Romero as Chief Joseph. It is a dramatization of Chief Joseph's resistance to the U.S. government's forcible removal of his Nez Perce Indian tribe to a reservation in Idaho.
Commander "Doggie" Kruger is this in Power Rangers SPD, following the loss of his planet and his people at the hands of Emperor Gruumm. The two-parter "Shadow" has him changing his mind.
An identical incident to Gus Griswald below occurred with Moze in Neds Declassified.

Music

Referenced by name in the song "Pioneer Square" by Reilly and Maloney, as a quote from a man named Joseph (either the Biblical figure, the Indian chief, or possibly a homeless man).
Phil Ochs' song "I Ain't Marching Anymore", written during the Vietnam War is told from a perspective of a soldier who was present at every American war since the War of 1812, but refuses to fight anymore.
Oh I must have killed a million men
And now they want me back again
But I ain't marchin' anymore.
The titular character in the Electric Light Orchestra song "Boy Blue." He returns home after fighting in an unspecified war and is welcomed as a returning hero, but in the last verse, after recounting all of the horrors that he saw and experienced, he flatly tells the crowd, "Hear this clear, for I'll not further say/That no man, shall cause me to take up arms again."

Video Games

Karel in Fire Emblem: Sword of Seals. Blazing Sword, the prequel, shows us what he retired from.
- Ike from Fire Emblem: Path of Radiance and Radiant Dawn also left Tellius after the war was over.
Lt. Velasquez near the end of Traffic Department 2192... after having spent most of her life on a Roaring Rampage of Revenge over her father's death, she's looking at an absolute victory, having defeated a galaxy-spanning army practically singlehandedly - but losing countless friends along the way. When the opportunity comes to actually kill the Emperor, she demurs - all she wants at that point is for the war to end, and killing him would merely create a vacuum for some other power-mad leader to step into.
The Vell-os from Escape Velocity: Nova surrendered to the Colonial Council and became slaves, because the alternative was to fight the Colonial Council and win, causing immeasurable death and destruction.
At the end of Assassins Creed Revelations, Ezio decides that he has seen enough action as an Assassin and leaves his weapons behind to start a peaceful life with Sofia. He is forced into action one last time in Embers when a young Assassin seeks his advice on rebuilding the Order in her country and he dies not long after.
In Call Of Duty Black Ops 2, specifically the endings in which Alex Mason stays dead, David Mason vows over his father's grave that he'll never fight again, too wearied by the war with Menendez to go on living the life of a soldier.

Western Animation

Leegolas from Bender's Game vows not to kill anymore after slaughtering the obnoxious but innocent Zoidberg monster.
Parodied in Rugrats in which Chuckie, scared out of his wits after a slide accident^*, dramatically declares that he will slide no more forever.
Adventure Time has Billy who becomes this after reaching the Despair Event Horizon.
Recess has this happen to Gus. Formerly known as "El Diablo" for his skilled, yet ruthless dodgeball playing, he vows to never play again after accidentally injuring an innocent bystander.
- This was parodied in "I Will Kick No More Forever", when star athlete Vince was outkicked by Alpha Bitch Ashley Q. and quit playing kickball "forever".
One Tom And Jerry "Mouseketeer" cartoon "Tom and Ch�rie" features Jerry's pupil (Tuffy) shuttling letters back and forth between Jerry and his current romantic interest. However, each time he sets out, he gets challenged by Tom and has to fight his way back and forth. It keeps going throughout the cartoon until Jerry supposedly gets a "Dear John" Letter. But... Jerry just changes romances and it keeps going. This time, however, when Tom challenges him, Tuffy ignores it. When challenged again, Tuffy basically tells Tom "Foo!" and leaves, ending the cartoon.
In Kung Fu Panda Legends Of Awesomeness, this is the eventual decision by Peng in his second appearance, as he's afraid kung fu will fuel his inner darkness and he must forever give it up to protect the people he cares about, despite Po's objections. With the whole premise of the show being kung fu, this is shocking for how it was played straight.