Mysterious Protector

""Oh look, it's the mysterious powerful ally that follows us around but doesn't really join our group!" "That's right, I am the mysterious powerful ally that follows you around but doesn't join your group!""

- Boy and Robot's Epic jRPG Quest

A common element in Shojo stories, particularly of the Magical Girl variety: the secretive figure who appears in a moment of need, aids the heroine, and then vanishes again. He doesn't always do much—a word of advice or encouragement, or a single attack that distracts the enemy for a critical instant—nor does he even have to be even as powerful as the heroine. But his interventions are critical to her survival or the maintenance of her morale.

While his true name and nature are usually concealed in the beginning, the heroine eventually finds out who he is about two-thirds of the way through the series. Subsequently, he often becomes her love interest. For some reason, he usually gets possessed or otherwise has to work against her for a time. As his rescue is inevitable, he becomes a little prize for the heroine's hard work.

Subtrope of Mysterious Watcher. Compare Aloof Ally, his Distaff Counterpart who becomes a member of the team instead of a love interest, and Enigmatic Minion, the villainous version.

Anime and Manga

 * Tuxedo Mask from Sailor Moon pretty much epitomizes the trope, although his counterpart from Pretty Guardian Sailor Moon is anything but.
 * The Moonlight Knight from the Makaiju arc of Sailor Moon R.
 * Codename: Sailor V has Kaitou Ace who on a few occasions appears as Sailor V's Mysterious Protector, but he's also the main character of a Show Within a Show and thus is simply an actor who V meets and is aided by a couple of times. Until it turns out he's.
 * Ferio from Magic Knight Rayearth.
 * The prince who rescues Utena at the beginning of Revolutionary Girl Utena, and inspires her to become a prince. Not a love interest.
 * Vega from GEAR Fighter Dendoh early on, though she becomes a combatant later.
 * Haji during a good part of Blood+.
 * Ao no Kishi/Blue Knight in Tokyo Mew Mew. Alto the cat may also qualify.
 * Mihara Oujirou in Angelic Layer is a shounen example, although the main character is still a cute girl.
 * And Oujirou's brother, Icchan, is a non-romantic example.
 * Hayate the Combat Butler parodies this in an early episode; When Hayate is about to be taken away by the "Very Nice People", Nagi shows up wearing a goofy mask and calling herself "Mask the Money".
 * Haku in Spirited Away certainly counts, although his development happens over the course of a single movie rather than a TV series.
 * He helped Chihiro several times throughout the course of the movie, remarking that despite not remembering anything else about his past, he remembers her. It is later revealed that
 * In Magical Girl Lyrical Nanoha A's, a mysterious masked man shows up to protect, err, the villains. From Nanoha. But that's a detail.
 * Limone in Wedding Peach. Though here.
 * Far from romantic, and the series is heavily Seinen, but the Skull Knight in Berserk is the reason that Guts decided to go back to the Band of the Hawks after leaving Griffith, and.
 * Female, non-shoujo example: Miyu from Mai-Otome has helped Arika out of a jam or three before simply disappearing to goddess-knows-where.
 * Tooya from Ayashi no Ceres. Bonus points for wearing a Badass Longcoat, shades, and for being stoic.
 * Tamahome of Fushigi Yuugi sort of falls into this trope at first. "Sort of" because Mysterious Protectors don't usually ask for money back, and because we get to know who he is soon enough.
 * Nakago briefly plays this role for  after he swoops down and   when she was searching for Miaka.
 * In Umineko no Naku Koro ni, Gretel/Ange Ushiromiya is an odd example because she's both female and non-romantic (Because of her true identity). However, she matches this better than Aloof Ally in the types of interventions she does, in the secret identity aspect, and in the fact that she makes it expressly clear in the beginning that she sides with Battler, not just that her goals are similar. Also a little odd in that.
 * Invoked in Mahou Sensei Negima; when Negi was a (younger) child, he viewed his father like this, to the point of getting himself in trouble so that his father would come save him.
 * sorta takes this role in one of the animated series.
 * Meta Knight from the Kirby anime, at least for the protecting part.
 * a Shonen example would be Phoenix from Metal Fight Beyblade, who is later revealed to be
 * Played straight in one episode of Pokémon, until the end when the cloaked hero is revealed to be . Who else?
 * Kakeru, the protagonist of the sports manga Area no Kishi, stopped playing football in grade school after injuring another player, and has been unable to bring himself to play again since. After being chewed out by his older brother Suguru for holding himself back, Kakeru encounters a mysterious masked football player in a nearby park, who challenges him to a one on one night game. Though Kakeru was unsure of the player's identity after leaving, the challenge helped to re-awaken his love for playing the sport.
 * Speed Racer: Racer X.
 * Honey Honey no Suteki na Bouken has Phoenix, a Gentleman Thief with a Domino Mask not dissimliar to Tuxedo Kamen—but much earlier; he shows up to help Honey in the nick of time during her wacky adventures, not that she always wants to help.
 * Knight Schumacher in Future GPX Cyber Formula, at least in the TV series. As the protector of the Sugo Team, he makes sure that no one can steal Asurada.
 * Although he didn't make a habit of it, Dragon from One Piece was introduced as Luffy's Mysterious Protector before
 * Homura from Puella Magi Madoka Magica self-consciously tries for this trope. That and the Batman entrance/exit syndrome.
 * Air Gear has Ringo dress up in a swimsuit and a variety of items from the school drama department closet, takes the chip out of her Air Treks, and calls herself Swimsuit/Croissant Mask to help Kogarasumaru in its early days. She dons the disguise (which fools the more idiotic characters but not the more intelligent) in order to hide her awesome abilities from Ikki.
 * Yami Yugi is this for Tea at the start of the Yu-Gi-Oh! manga - for a long time, due to the circumstances, she never saw his face, and she ended up falling in love with his voice. It was only later that she realised that he was actually the alter-ego of her childhood friend. Also, he can count as this for Yugi as well - in the early chapters, Yami would possess Yugi when he was needed and he'd deal with the threat...meaning that to Yugi, he would suddenly black out and wake up to find that whatever problem was stressing him out is gone somehow.
 * In a rather odd variation, odder for being in one of the bloodiest and mindscrewy Seinen out there, Ran and Ichise Texhnolyze are this from each other. Ran, resident Mysterious Waif, is the more traditional version, distant and mysterious, appearing to guide or help Ichise out suddenly at pivotal and critical moments, before fading away into the background, remaining almost anonymous until at least halfway through the anime. Ichise, on the other hand, is dark and quiet Determinator who tends to show up mysteriously at the right moments through more sheer luck than anything else (while all of Ran's appearances are intentional, as far as we know).
 * Misty Knight from Kaitou Tenshi Twin Angel.
 * Some Pretty Cure uses this:
 * Heartcatch Pretty Cure has the Zetsubou-sensei Kamen. This being HCPC, the Cures ultimately must beat him in a battle to prove that they have grown stronger than him.
 * Suite Pretty Cure: Cure Beat. Which is not Hummy.
 * In Transformers: Robots in Disguise, Ultra Magnus is this, though his attitude toward them is less mysterious and more "I don't like the Autobots but... I guess I shouldn't let them get vaporized."
 * Zero fulfills a similar role for Nunnally in her manga spinoff: Nightmare of Nunnally... sort of. He shows up out of nowhere whenever Nemo is in the middle of a battle, and usually brings about chaos, allowing Nemo to win or escape. It can be seen most obviously near the end, where Zero acts as a Supporting Leader along with Euphie, Suzaku, and their combined armies.
 * Digimon Adventure: After the Chosen fall apart following Taichi's disappearance, Sora completely disappears and acts in this capacity, working to get everyone (except herself) back together in the face of PicoDevimon's trickery tearing the team apart.
 * Syaoran Li from Cardcaptor Sakura generally fills this role. Although his initial plan is far from acting as Sakura's protector, he often ends up helping her out with moral support, needed information, and the occasional spell. When he enters, he is much more of a mysterious rival, but nonetheless fits the typical presentation of the trope to a tee in the long run: he is less powerful than the heroine, but plays a small role in many of her battles (often to boost her morale or give her a new idea); he is at first very mysterious and seems to be watching the heroine; and in the end, he becomes her love interest.

Comics

 * "The Fox" in Floyd Gottredson's Mickey Mouse comic Death Valley.

Film

 * Lo, from Crouching Tiger, Hidden Dragon plays to this niche admirably in an early fight sequence. He obviously lacks the firepower to stop any of the major fighters of the setting, but he only needs to provide a few seconds of distraction to allow his love, Action Girl Jen Yu, to escape.

Literature

 * Sailor Nothing subverts this one hard. In the backstory and beginning, Magnificent Kamen would show up to help the heroine when she's fighting monsters she can't handle herself, but he's a scheming bastard who has no qualms about killing civilians and even ex-Sailors who have seen too much or outlived their usefulness, and towards the end
 * Welstiel Massing from The Saga of the Noble Dead is also a subversion- he appears at convenient intervals, gives Magiere much needed advice about fighting vampires.
 * Mr Carrisford in A Little Princess watches over Sara without her realizing that it was the man next door to the school who was secretly delivering presents and gifts up to her room to keep her spirits up.
 * In The Chronicles of the Deryni, Morgan and Duncan are met a few times by a mysterious man who appears to be Saint Camber. In High Deryni, this person warns them about other Deryni mages who might challenge them to test their powers. In the climax of High Deryni, he reveals himself.

Live Action TV

 * The Haitian from Heroes could've been the Trope Namer. Tall, Black, and never speaking, nobody had a clue what this dude's agenda was. Just when it looked like he was about to finish Claire (the immortal cheerleader), turns out he's her appointed protector.
 * Angel from season 1 of Buffy the Vampire Slayer. Fitting, considering Joss is a fan of Sailor Moon and the first few seasons of Buffy can be seen as a warped, live-action magical girl show.
 * Non-shojo version: Both the Gold Ranger of Power Rangers Zeo and the Phantom Ranger of Power Rangers Turbo, who would appear to save the Rangers and then vanish. They each wound up having to be rescued by the Rangers they zipped in to protect. It was in that arc that we learned who the Gold Ranger was, and almost learned who the Phantom Ranger was. The Omega Ranger of Power Rangers SPD started out this way as well, as did the Gold and Silver Rangers of Power Rangers RPM.
 * Doctor Who, "The Girl in the Fireplace". Inverted in that we see it from the side of the Mysterious Protector himself.
 * In Misfits, the mysterious "Superhoodie" keeps showing up to save the Misfits, and seems to know an impossible amount of information about them.

Video Games

 * In Fire Emblem: Radiant Dawn, this trope is possibly subverted. A major, presumed dead antagonist from the previous game actually plays this role to the hilt with the new protagonist, Micaiah.
 * Subverted in Betrayal at Krondor: After being captured and brought to the fortress in the heart of enemy territory, Gorath and Owyn are mysteriously set free - the doors to their cells open by magic. Later attempts to discern the identity of their mysterious saviour turn out to be fruitless. In retrospect, it seems obvious that the one responsible was
 * Fallout has a perk which causes a "Mysterious Stranger" to appear and assist the character randomly in battles.
 * Fallout: New Vegas also has 'Miss Fortune', essentially a female version of the Mysterious Stranger dressed in a Vegas Showgirl getup, and causes collossally bad luck to occur to a foe instead of outright killing them.
 * The Mysterious Stranger can also occasionally serve as an inversion as he is infamous for accidentally shooting the player in the back with sometimes fatal results.
 * Maybe that's because if he appears when you fire a shotgun or an explosive in tight quarters you often hit HIM
 * Early on in New Vegas, if the player is having trouble, Victor the robot cowboy will show up to help fight off your enemies. While he accredits this to being a generally good-natured robot, the truth is that Mr. House is using him to make sure that you make it to Vegas.
 * In Honest Hearts, you can learn about Randall Dean Clark, a former US Marine turned survivalist who eventually became this for a bunch of children, watching over them and giving them supplies and books while remaining unseen to them. In the end, you find his skeleton on the
 * Proto Man this role after the end of Mega Man 3, showing up right after you hear his signature whistle.
 * Mega Man Star Force, like the Doctor Who example above, is shown through the eyes of the Mysterious Protector himself. This occurs as he (Mega Man Geo-Omega) has to protect Luna Platz from danger. This is reversed three times. First, in the first game as she merges with one of the evil FM-Ian warriors, forcing him to battle her. Then in the second game when the OOPart turns him into a wild EM wave being, causing him to attack her (he gains control over the object)..
 * Mickey Mouse (Yes, the Mickey Mouse) serves this role during certain boss fights in Kingdom Hearts II. Get killed during certain encounters and you have the option of having King Mickey rescue you. (He is far more Badass than you'd expect any Disney character to be.) Now, obviously Sora, Donald, and Goofy would recognize the King when they see him (He's kind of hard to miss, even with the ridiculous Black Cloak), but he always seems to teleport away immediately after rescuing Sora, so it's never made quite clear if Sora is aware the King is following him around. His rescues are more of a gameplay mechanic rather than an actual element of the plot.
 * Unfortunately, the chances of him appearing in later fights goes down every time he rescues you. If he's saved your ass once or twice, he's unlikely to do it again, possibly because he's becoming too worn out between world-traveling and fighting (though again, it's a gameplay mechanic, so it's possible that the programmers simply didn't want to promote too much laziness as he is rather powerful and it is sometimes better suited to the fight then Sora and Co. He can't actully kill anything however, his move list lacks a finishing move which is required for the final blow on bosses, planting him even further into this troupe.
 * Lloyd Irving, the protagonist from Tales of Symphonia, plays this part to Genis and Mithos in an optional sidequest. Mithos being a powerless tyke and Genis being a decent mage but not the best fighter in the world  saving them from monsters and the such.
 * In Final Fantasy VI, Shadow will join and leave the team at various points in the game, coming and going as he pleases. You'll eventually have an opportunity to add him to your permanent roster, though.
 * One shows up during one of the first missions of X2: The Threat, if your ship takes too much damage.

Visual Novels

 * Rider in Fate/stay night when she finally gets to move into the main storyline. Even then she's not actually in focus a lot of the time, preferring to be invisible. But she saves Shirou several times and then vanishes without really telling him anything. As for the love interest part... Well, it's pretty clear she's at least somewhat attracted to him.
 * Somewhat attracted to him? This is Emiya Shirou we're talking about; EVERY female is attracted to him.
 * In Under the Moon, Zero appears out of nowhere to bail the heroine Ashe out of some tight spots, but disappears just as quickly.

Web Comics

 * No Need for Bushido gives us Matrix who can't stop herself from meddling in an as-of-yet unspecified bet that she made.
 * Elan said Therkla was one in Order of the Stick.
 * may be one, after this Wham! Episode of Looking for Group.

Western Animation

 * Zuko from Avatar: The Last Airbender becomes "The Blue Spirit" to save Aang in an episode of the same name (although he wasn't mysterious for long), and later to free the Avatar's flying bison Appa in season 2. Of course it's just because he wants to make sure no one else gets the credit for catching Aang. This is exaggerated in "The Ember Island Players" enough to make Zuko and Aang... uncomfortable, for obvious reasons.