In the End You Are on Your Own

"Angelus: That's everything. No weapons, no friends, no hope. Take all that away, and what's left?

Buffy: [Barehanded Blade Block] Me."

- Buffy the Vampire Slayer, "Becoming, part 2"

As a Stock Aesop, believing in the Power of Friendship over isolationist self-reliance is pretty standard and true. There's a lot a group can accomplish that the individual(s) acting on their own can't. In fiction, Friendship even brings tangible benefits like a Five-Man Band developing an Attack Pattern Alpha which uses All Your Colors Combined. Some shows may even go the extra length to crush the message into a viewer by having a Sixth Ranger fail miserably and join the team. Once the Season Finale rolls around however, The Hero can't depend on his weak friends to keep up, and will have to fight the Big Bad Final Boss on their own.

While The Hero is usually the strongest out of the group, many shows will switch gears abruptly to have them fight the last battle on their own. Be it due to a Battle Royale With Cheese waylaying all their allies (or worse, In the worst case, killing them all), or because the enemy is so strong anyone else trying to help the hero would just become a meat shield at best and a dangerous distraction at worst. This limits the rest of the cast to cheering from the bleachers (maybe verbally slapping some sense into a hero woozy from a Hannibal Lecture) and perhaps acting as fuel a Combined Energy Attack or Super Mode. And that's it.

They will spend the rest of the battle just standing there and commenting.

Some stories work this into a narrative more organically. The Big Bad may cleverly isolate the hero from his friends via framing him or capturing them (and force them to watch him kill their leader). Then again there really are some challenges a hero Has Got To Do Himself, and being helped beat this enemy will cheapen their storyline. In these cases the value of friends isn't in their tangible help fighting but by placing their trust in the hero's success, motivating them to do their best. Trust is a powerful force like that.

Compare Duel Boss (who is not necessarily the Final Boss, as per this trope). See also What You Are in the Dark. Not to be confused with Dying Alone. Sub-Trope of Solo Sequence.

Anime and Manga

 * Dragonball Z basically slowly killed the cast (again) throughout the approach to each Big Bad (Frieza, Cell and Buu). By the time Goku fought Frieza and (almost) killed him, they were the only two people on Namek, the rest being dead or on Earth. A larger cast lived until Gohan beat Cell, but they were just on the sidelines by then. For Buu, literally everyone that wasn't a Kai, Goku, Fat Buu or Mr. Satan (or the puppy) was dead. Including one of the combatants (Vegeta). Dragon Ball GT didn't kill the cast as much, but the Big Bads were so powerful by then that nobody that wasn't Goku or SS4 Gogeta was pretty much helpless (besides for Trunks during the Black Star Dragon Balls part and Pan every once in a while).
 * Every episode ever of Sailor Moon; you start to wonder why she needs a team.
 * Protection.
 * Without the other Sailor Soldiers there to fight the monsters until she arrives, they would have attacked innocent people.
 * Digimon Frontier. By the end of the series only the lead and lancer could fight the Big Bad since their ultimate Super Modes required all the other members of the band to give them their spirits (ability to transform). Though this may have later become a subversion considering that the actual final battle was Big Bad v.  but you know, Your Mileage May Vary.
 * Saint Seiya sometimes used this trope, sometimes not. Frequently Seiya would be the last Saint standing against the season's Big Bad, and (if any of the others were conscious/alive) they'd boost his Cosmo with theirs. A few times though they would gang up on enemies, but by and large one-on-one battles were the norm.
 * Yu-Gi-Oh!, however, the team often gets their day in the limelight, but they get hurt so often it's a wonder that Yugi lets them come along at all. Given that Duel Monsters is for the vast majority of the time a one on one card game, this is true pretty much every episode.
 * Somewhat justified in Zettai Karen Children... while Za Children generally work as a team, Kaoru is always their heavy hitter, possessing the most in-your-face offensive power - Telekinesis. When fighting Mooks or generally low-level foes, the other two will join in with creative use of their 'utility' powers (Teleportation and Psychometry, respectively). But when the big hitters show up and it's time for a boss-fight, they know that it's better to stand back and let Kaoru do what she does best - sometimes providing intel or a quick escape to aid. In the later season, it's taken to its natural conclusion, with a special device that basically saps Aoi and Shiho of their Psychic Powers to pool it all in Kaoru, giving her access to her Badass, Power Gives You Wings Queen Of Catastrophe form, which makes her basically unstoppable, and able to do several things that are otherwise considered theoretically impossible...
 * At the end of the Soul Eater anime,
 * An ending which departs from what the manga and most of the anime emphasised as necessary, as well as strength, for victory - teamwork and mutual understanding.
 * In Advent Children, the FFVII crew decide to let Cloud battle Kadaj on his own.
 * Not that any of them had much choice, with Cloud chasing Kadaj across half the continent trying to stop him from using the Jenova cells no one else really had any hope of keeping up. And of course by the time any one else might have been able to finally track them down, Kadaj had already used the Jenova cells and taken on the Memory of Sephiroth. Anyone in their right mind takes one look at that brawl and promptly says fuuuuuck that.
 * Macross Frontier: The Wings of Goodbye leaves Alto to square off alone against Brera's FAST equipped VF-27, a squadron of V-9 Ghosts, and while everyone else just watches (or sings).
 * Massively subverted in the finale of Inuyasha -
 * In the manga and second anime of Fullmetal Alchemist, the battle against  starts off as a major affair, with everyone getting in their shots. But after.

Comic Books

 * In the Books of Magic series, at one point Tim is caught in a pattern based off old fairytales and is reminded that common element of many folk stories and fairytales is that while the hero gains companions and tools that help him reach the Big Bad, in the end it comes down to just his own courage, after companions and tools are stripped away - What You Are in the Dark is what must win the day.
 * Discussed and deconstructed in Watchmen: When a young boy called Bernie asks an old man also called Bernie for help, he denies it claiming that young Bernie needs to learn that "in a final analysis, we are all alone". Then Old Bernie sees a paper and it’s eager to help young Bernie. The paper said that the Russians have invaded Afghanistan and that means World War III. After young Bernie leaves, Old Bernie monologues that "we are here to help each other… in a final analysis".

Film

 * At the climax of Return of the Jedi Luke deliberately goes without the aid of his comrades to confront Darth Vader and the Emperor.
 * At the climax of Labyrinth, where Sarah must face Jareth alone, "because that is the way it is done."
 * In Serenity, Mal must fight the Operative alone because the crew is buying him time by holding the line against the Reavers. And at the end of that fight, River has to fight against the Reavers by herself.
 * In Delgo, Delgo's dying father tells him "You're on your own, kid."
 * Villainous example. In the Daredevil movie, Kingpin sends his guards home so he can face Daredevil alone.

Literature

 * Harry Potter generally ends up in one-on-one fights with Voldemort. In the first book it's because only one person could make it through to the Philosopher's Stone, but in The Movie Hermione purposely leaves him because This Is Something He's Got to Do Himself. In later books, events continue to conspire to cut him off from any allies who set out with him.
 * Then again, divide and conquer is Voldemort's preferred way of handling things in the first place.
 * In Thursday Next quite often, very much the final battle with Adornis Hades.
 * The Bartimaeus Trilogy features Nathanael and Bartimaeus. Considering they end up  this is also a Dying Moment of Awesome. Your Mileage May Vary because no one knows for sure if it wasn't a Dying Alone Moment
 * This is practically Tiffany Aching's motto, but she chooses to be fiercely self-reliant. As she puts it, "A witch deals with things."

Live Action TV

 * Yuusuke/Red Falcon from Choujuu Sentai Liveman is the only human left unaffected by Bias' Mass Hypnosis, leaving him to defeat Bias alone, in a sense.

Tabletop Games

 * The Tournament of the Dragon Adventure for the 3rd edition of the Champions RPG involved a martial arts Tournament Arc that culminated in a solo battle against an entity known as the Dark Dragon. The mystic nature of the Dark Dragon made him grow stronger with every foe attacking him at once, making him a horror to battle with an army, but when faced by a single opponent, he was at his lowest power levels, thus justifying the creation of an tournament to find a worthy warrior to battle him one-on-one.

Video Games

 * The trope namer is The Longest Journey, where April IS on her own in the end, though not in the Final Battle kind of sense.
 * Both Knights of the Old Republic allow you to have your party fighting alongside yourself for most of the game, then render them unable to join your for the final boss.
 * The second game is particularily cruel, since it abruptly drops you on Malachor V. Your character wakes up and has to spend the entire level on their own, even though it is made perfectly clear that the rest of your crew survived and got out. At least in the first game you could have two party members with you for most of the Star Forge until your fight with.
 * This might have had to with early plans for the game, in which there were a few scenes on Malachor V focused on other characters, depending on the choices made by the player over the course of the game, such as a fight between Atton and Darth Sion which could end either with him surviving and reuniting with the Exile, or losing and dying in her arms, or if the player was a dark side female and fell in love with the Disciple.
 * In Sonic the Hedgehog 2, if you're playing with both Sonic and Tails, Tails will be unplayable during the last two levels.
 * Similarly, In Sonic 3 and Knuckles, Tails will disappear after the first of the three final bosses is defeated, leaving Sonic to fight the last two on his own.
 * And finally, in Sonic 3 & Knuckles, Tails won't be able to accompany Sonic into the Doomsday Zone, the final level.
 * This trend takes up in the later games as well. In Sonic Adventure Super Sonic has to take on Perfect Chaos on his own.
 * In Shadow the Hedgehog Shadow is forced to fight Devil Doom on his own, despite the abundance of characters in the game.
 * In the arcade TMNT, teamwork doesn't work on most of the bosses. You're actually better off taking one player, running a pattern on the boss (usually hit, walk back, up, or down), and keeping everyone else back. Done correctly you can beat most bosses without losing even one bar of energy. If more than one player attacks a boss, the boss will just spam attacks that knock everyone out.
 * The final area of Super Paper Mario has each of your companions having to leave one by one to allow you to continue, leaving you alone when you fight the boss..
 * In The World Ends With You Neku attempts to invoke this by leaving Shiki and Beat behind unconcious and confronting the final boss but it becomes Subverted when they catch up with him and tell him off for running off on his own just before the fight starts.
 * Mother 3 handles this is a different way for the end Duel Boss battle, in that the Masked Man uses a lightning attack that will always knock out anyone on your team still standing besides Lucas, who's carrying a Deflector Shield.
 * So long as you are nice to your companions in Neverwinter Nights 2 Mask of the Betrayer, they stick with you until the bitter end. Except that during the final Battle in the Center of the Mind you are forced to face the Betrayer alone, or with your Love Interest if you have one on your team.
 * Jade Empire lets you have a teammate with you during most of the game, but forces you to take on Sun Hai and on your own.
 * Age of Pirates 2: The City of Abandoned Ships plays this one extremely jarringly. The game allows the player to have up to three hired blades follow them around, but in scripted quest-related fights they are often inexplicably absent, leaving the player to face often overwhelming odds on their own, even though that's precisely why he or she hired the thugs in the first place.
 * In the end of Breath of Fire 4 when you get to the Emperor's Fou-Lu Throne room he simply knock off every party memeber leaving only Ruy to face him in a Duel Boss.
 * Subverted in Breath of Fire 2 for the final boss.  until you use the Power of Friendship to return your friends to you.
 * In Star Fox, Fox has to fight Andross alone during the final battle.
 * However, in Star Fox 64 Fox chooses to fight Andross alone, there was no real need for him to do so.
 * The final battle of Persona 3 is the main character against . Nobody can come with him. In a moderate subversion, however, his weapon against the final opponent is the hopes of everyone he met on the way to the confrontation.
 * It gets repeated in Persona 4 right down to the letter
 * In the Turai Ossa mission of the Guild Wars Bonus Mission Pack, you leave your followers to fight Palawa Joko one-on-one.
 * Averted big time in Baldur's Gate 2 where The Hero gives each party member a chance to leave the party while they can before the "final" confrontation with the Big Bad. Not even the biggest bastard from hell leaves his (or her) side.
 * Invoked in  ~Assassin's Creed: Brotherhood~ .
 * The Final Battle of Ace Combat Zero is fought without a Wing Man or any allied aircraft support (except AWACS) at all, because . Ditto the fight against the True Final Boss in the Bonus Level.
 * Mass Effect 2 kinda has this with the Arrival, its final DLC mission, which has to be completed by Shepard alone (except a few Escort Mission-esque levels with a Guest Star Party Member). Though, of course, true to its Wide Open Sandbox gameplay, you can complete the assignment at any time, even before the Suicide Mission (which kinda misses its entire point).
 * The Overlord DLC plays this perfectly straight by unexpectedly trapping both your squadmates just before the Final Boss, so Shepard has to take on him/it alone.
 * Likewise, Mass Effect 3 plays this perfectly straight for the first time in the series proper.
 * In Kingdom Hearts, when Sora goes to fight Riku possessed by Ansem, a barrier pops up, separating him from Donald and Goofy, forcing him to fight alone. Later on, said barrier pops up again during the fight with Darkside Heartless and the subsequent fight with Ansem. However, Donald and Goofy manage to eventually rejoin the fight after Ansem enters his One-Winged Angel form.
 * Very much averted in Overlord. When the Big Bad emerges and you lose control of your Minions, it's only moments before you start regaining them and lead your horde to victory.
 * At the end of Diablo III,
 * At the end of Diablo III,

Webcomics

 * Klaus Wulfenbach from Girl Genius was just the trusty lackey to the Heterodyne Boys when he was younger. When he came back from his offworld expedition, everything had gone completely to hell and the Boys were nowhere to be found. Klaus put the world back together alone. It worked.
 * In Impure Blood, Dara can get the gate open, but Roan has to get out on his own power.

Western Animation

 * In Avatar: The Last Airbender, Aang must eventually face the Firelord alone.
 * But not before his allies have recognised that while Aang must fight Ozai alone (reasonable in-universe, though they do briefly consider teaming up) there is another problem, the sheer scale of the Fire Nation assault on the Earth Kingdom. They began to tackle what they could before they even knew Aang was returning to fight.

Real Life

 * Solo sailing. 'Nuff said.
 * Classic dueling. You can have a second, but the second's there mostly to hold your coat or take care of your body if you lose.