A character archetype that frequently appears in The Hero's Journey, the Mystical Waif is usually a physically young girl (although she may be Really 700 Years Old) with a plot-significant power. While most commonly female, a Mystical Waif can be male, as long as he evokes feeling of protectiveness.
Ofttimes, she's a part of some mysterious, previously unknown society or race that possesses great magic, and she's not uncommonly the last of her kind. The bad guys usually want to exploit her powers to control/destroy the world, while the heroes want to save her out of chivalry or general contrariness.
Typically introduced as a part of the Call to Adventure, the Mystical Waif often appears to the hero seeking for his help while providing him with an exposition to the unknown aspects of their universe. Her introduction is what usually propels the plot from random adventuring to serious world-saving, as she recruits the rest of the party to help her collect the crystals, and she may spend some time as a Damsel in Distress before eventually joining the Heroes' team. If the story includes romance, she may eventually develop to be the Hero's Love Interest, or at least a contender for one.
Personality-wise, the Mystical Waif is usually pure-hearted and kind, although she may seem a little distant at times. She is also extremely naive about the world, and unfamiliar with even the most basic facets of the characters' lives — that is, she has No Social Skills, which can be Played for Laughs in the more light-hearted parts. She might not even speak the same language as the main characters' during her initial introduction to further highlight her cryptic nature. She can be selfless to the point of self-sacrifice at times.
Sure signs you're dealing with a Mystical Waif are odd hair colors; weird (by the standards of the fictional world), often futuristic-themed clothing; magical powers; blank, serious facial expressions; lots of ellipses in her speech; and an inordinate amount of attention from the villains. Frequently overlaps with Mysterious Waif, especially if her past or identity is kept hidden for most of the story.
She is a stereotypical party member in many RPGs. Gameplay-wise, the Mystical Waif is almost always magic-oriented, usually doubling as a White Magician Girl, or if more proactive, as Barrier Warrior or Squishy Wizard. She'll have weak physical stats, but strong magical stats and average-or-better speed. Her quality as a game character is almost entirely tied up in how powerful her attack spells are and whether anyone else has the ability to heal.
- Yui in Sword Art Online is the textbook definition of this trope. A mysterious girl found wandering in the woods with no memory of how she got into the game, Asuna and Kirito quickly discover her secret powers when she confronts a power dungeon boss that downed both of them and take it out almost effortlessly.
- Hotaru Tomoe/Sailor Saturn from Sailor Moon seems to have many characteristics of this trope. She is mysterious, ready for a self-sacrifice, and wears unusually dark clothes; she also has several mysterious powers even outside of her Sailor Senshi identity (although many of the other girls did too). Her situation is somewhat different, as there are three sides involved: Sailor Moon, who wants to save her; the Guardians of the Outer Solar System, who want to get rid of her as she poses a threat to the world; and the evil Death Busters, who want to destroy the world with her help. A couple seasons later, she joins the main cast, and her powers overlap somewhat with those of the White Magician Girl Cool Big Sis, Sailor Pluto.
- Yagami Hikari from Digimon Adventure and Digimon Adventure 02, the human lightbulb. Also an Ill Girl, she is the only one to have a Crest (Light) that doesn't refer to an innate virtue or trait. The powers of this Crest usually manifest themselves in weird ways, and she has been shown as both 1) unusually self-sacrificing and 2) drawn to the Dark Ocean, because of her powers and walled-in emotional problems. She's also empathetic to the point of being borderline psychic, which sends her into two Heroic BSODs in 02 (and during the last one, her best friend Miyako has to literally bitchslap her back to sanity).
- Reverie "Ren" Metherlence of Elemental Gelade is a mysterious and legendary weapon who is frequently rendered helpless and constantly protected by the main character.
- Kisara of Yu-Gi-Oh!, the white-haired and blue-eyed Egyptian and homeless, quiet, vaguely psychic, mysterious keeper of the spirit of the Blue-Eyes White Dragon who sacrificed herself to protect the only person who ever showed her kindness, High Priest Seto...
- Vivio of Magical Girl Lyrical Nanoha Strikers, the main character's adopted 6-year old daughter who has differently colored eyes and was found trudging through the sewers while chained to a pair of cases containing Relics. She turns out to be the clone of the Sankt Kaiser, required by the Big Bad to activate the Saint's Cradle and packing enough power to match Nanoha blow for blow.
- Yukina from YuYu Hakusho appears young but, like her brother Hiei, is a demon and therefore may be much older than she appears. She is pure-hearted, kind, distant, naïve, and has blue (or, arguably, sea-green) hair. She is targeted by villains either for her gem-making powers (They come from her tears! Awwww!) or because the main characters care about her and she is no Action Girl. She occasionally serves as the group's healer, due to her abilities in that field.
- Lala Ru from Now and Then, Here and There, who possesses the power to control water using a pendant that contains a vast reservoir of water. However, unlike most examples, she is neither pure-hearted nor kind. In fact, she hates all of humanity due to the utter HELL they put her through, and refuses to save the planet even though she has the power to do so. Until later, of course... but even then, you wish she hadn't.
- Wendy from Fairy Tail has elements of this, including a Mysterious Past, bad guys wanting her (in the case of Brain), non-action status, bit of a Damsel in Distress, purehearted and kind, and The Medic.
- One of the very first Star Trek fan clubs, "Spock's Scribes", published a journal with satirical fan fiction about young women passengers on the Enterprise who cause trouble. Spock's human cousin Samantha Scott, written by the only adult member of the club, was definitely one of these. The daughter of Amanda's sister Amelia and a Dr. James Scott (no relation), both physicians on planet XX Larid, she was Raised by Natives after her parents died in an earthquake, and picked up Psychic Powers from them. She caused and attracted random chaos on the ship.
- Flute, in The Elenium trilogy by David Eddings, is a small girl who is revealed, slowly, to have greater magical powers than anyone else in the party. She can control time and animals, among other things. Eventually they find out that Flute is actually the goddess Aphrael, which explains everything.
- Luna Lovegood in Harry Potter Last of her line. Mother died when she was 9. Orphan's plot trinket = Butterbeer cork necklace and Dirigible plum earrings. Also pure-hearted and kind, distracted at times, weird, persecuted, absolutely adorable! Don't forget that she turns out to be pretty darned good at magic herself and can notice things that others don't.
- House of Many Ways features a little white dog who is actually named Waif, who had been living with Charmain's great-uncle William (Wizard Norland) for a short time. Waif is no ordinary dog, but a rare, magical enchanting dog. Later, we find out that Waif actually is the latest generation of the Elf Gift, which (or, as it turns out, who) is supposed to protect the royal family of High Norland. However, unlike most examples, besides having magical powers Waif does not act very mystical, but like an ordinary dog, who begs for scraps, overindulges on human food, and clings to Charmain who she has adopted as her owner.
- The Dresden Files: Through a horrifying series of events, the mantle of The Archive, the repository of all knowledge, was set upon a young girl. She can give a showing for herself in magical brawls set up as a trap for her personally.
- In Terry Pratchett's Discworld novel Monstrous Regiment, Wazzer Goom fits this trope, as the brutalised girl who becomes the spiritual channel for communications with the long-dead Duchess of Borogravia.
- Maia, the child with the ability of Precognition from The 4400 fits many of the characteristics of this trope, with her slightly creepy otherworldliness (and, of course, her potentially important ability).
- River Tam from Firefly is the youngest member of the crew of Serenity, and aside from being a peerless genius and psychic, she apparently can shoot people without even looking and defeat small armies of berserk space pirates in hand-to-hand combat without trouble.
Once, there was a maiden...
...who fled a shadow, in the company of a friend.
They traveled through strange places, and among strange people.
"How can you trust me," he asked, "with such horror behind you?"
"Love endures," she said.
— The Scripture of the Bride
- Fina from Skies of Arcadia practically defines this trope - she's a futuristically-dressed, kind, naive, shy girl with the highest magic attack and most potent healing abilities in the game, who is a descendant of one of the lost Ancient Civilizations and is doggedly pursued by the Valuan Empire (due to the fact that every member of her race gets their life force from one of the Silver Moon Crystals, and the only other member of the race the Big Bad has access to is The Dragon and is therefore not expendable) to the point that the game begins with botching the Valuans' first kidnapping attempt. The game revolves around her, in fact; the part of the game you spend neither helping her on her quest (which, to hammer the trope home, is to collect all of the Moon Crystals to stop the villains from using them to destroy the world) nor trying to save her is about one dungeon long, and it's at the very start of the game between bringing her to your hometown and the Valuans destroying it to get to her. Oh, and she's also one of the hero's two Love Interests alongside the Girl Next Door.
- Garnet from Final Fantasy IX — One of only two remaining summoners.
- Aerith from Final Fantasy VII — Last of the Ancients.
- Ellone from Final Fantasy VIII - mysterious past, flowing robes, special powers desired by both sides.
- Terra from Final Fantasy VI — Half-Human Hybrid of an Esper (the summons).
- Rydia from Final Fantasy IV — Last of the Summoners of Mist... thanks to the main character.
- Visas Marr from Star Wars: Knights of the Old Republic 2, though older than the archetype, otherwise fits this: she is sole survivor of the destruction of her planet, her species (Miraluka) are blind normally but "see" using the Force, and she speaks in strange ways. She can be sacrificed, if the player chooses to do so.
- Xenogears gives us Emeralda, who in addition to being Really 700 Years Old is a Voluntary Shapeshifter. She fits this trope so perfectly, it's damn scary.
- Isabella/Catleia from Advance Wars: Days of Ruin., though being from a strategy game she obviously doesn't have the RPG stats part of the trope, being instead a decent all-round CO with a Game-Breaker CO power.
- Mega Man Legends 2 has Sera, who plays the part perfectly, until after you collect the keys, when she takes over the ship and reveals herself to be the villain of the game.
- Alouette from La Pucelle Tactics hits enough of the required traits to fit here. Although not the last of her kind, she is found with amnesia, is mostly good with magic (although, as with all Nippon Ichi games, you can customize her as you like), is self-sacrificing and is the current Maiden of Light, even if she doesn't know it, which is a powerful position held only by one woman at a time and chosen directly by the Goddess.
- Avril from Wild ARMs 5 hits almost every single criteria for this trope. Silver hair, serious expression, unfamiliarity with customs, amnesia, sought by the antagonists, good with magic (although this is customizable), and Really 700 Years Old.
- Lufia herself (and her analogues in the other games). She is kinda out-of-place in human society because she's actually a Sinistral, and the other Sinistrals want her to help them stay alive and do evil things, of course. She is also portrayed as cute, innocent, and a love interest of the hero, and of course, has lesser physical stats but uses magic well.
- Subverted in Phantasy Star III with Maia, who is a mysterious, solemn, white-haired maiden who washes up on the beach, has no recollection of her past, and gets abducted by a dragon on her and Rhys' wedding day. Turns out the dragon is her shapeshifted brother, her amnesia was entirely mundane, and there's nothing unusual about Maia herself except that, of course, she's a princess. She doesn't even use magic.
- Julius from Sword of Mana is a very rare example, seeing as he's male and an antagonist to boot. He's still the Last of His Kind, exclusively uses magic, has a Mysterious Past, and is integral to the plot of the villain, who out-and-out hijacks his body eventually. His... uh, friend Dark Lord (the other main antagonist) seems to know exactly who and what he is and is implied to be sheltering him from the prejudice of the world while simultaneously keeping him from falling completely to evil.
- Shana from The Legend of Dragoon reeks of this trope. First she gets kidnapped and put in jail, then she turns out to be the moon child who will destroy the world. She exhibits the personality traits of this trope down to the letter.
- Despite being male, Joshua from The World Ends with You is a good example of this trope. He randomly makes a pact with Neku, is arguably Really 700 Years Old, and in a twist ending turns out to be the Big Bad, who does a Heel–Face Turn after the final boss.
- Sophie in Tales of Graces. Mysterious, plot-relevant past? Check. No Social Skills? Check. Futuristic clothing? Check. Lilac Rapunzel Hair? Check. She's everything but physically weak though.
- Anne in Mitsumete Knight. No wonder when you're a Cute Ghost Girl with heavy backstory, blue hair, mysterious atmosphere, and crucial importance to the heroine's and the game's storyline.
- Kingdom of Loathing parodies this with the Quiet Healer, who often drops the Amulet of Plot Significance.
- Rosalina, at least in Super Mario Galaxy, with her tragic backstory and enigmatic nature. Her other appearances eventually avert this, revealing she's quite a bit more resilient and playful than most examples.
- Kanna from Three the Hard Way She's a Really 700 Years Old alchemist, who is secretive and enigmatic in personality, and seems to know the Big Bad quite well. Gameplay-wise, she's a unique character with a relatively low physical and magical abilities, but can create and have access to alchemical weapons that can easily decimate Bosses. Despite being relatively useless in normal battles, one of the strongest party member actually remarks that they don't stand a chance against the Big Bad without her.
- Elizabeth from Bioshock Infinite fits this trop to a T: She had a sheltered upbringing (The only character she had a relationship with prior to the game start was a giant Bird-Man called Songbird); she is naive and tries to help the people of Columbia; she has mystical powers; is of huge interest to the antagonist due to her aforementioned powers (And to the protagonist due to actually being his daughter) and gameplay-wise she fits the support role, giving you medkits, ammo, and salts. She takes a level in cynic after she is tortured by Comstock on an alternate timeline.
- Fire Emblem Elibe has siblings Nils and Ninian in Blazing Sword and Sophia in Sword of Seals. All three of them are Really 700 Years Old Half-Human Hybrids, can sense the future and fit quite well story- and personality-wise. Furthermore, Nils and Ninian are strictly support units and are not able to attack or defend themselves (Sophia is a Shaman instead, but still falls under the Squishy Wizard category. She also has a healing touch, but in game proper, it's only used once and off-screen and promptly forgotten afterwards). Also, both Ninian and Sophia are possible Love Interests for The Hero of their respective game.
- Chains of Satinav has Nuri the fairy. The villain needs her for his evil plan (which involves an artifact that can only be used by a fairy, and she's the only one around), and has been searching for her. The main plot of the game gets into gear when the protagonist, Geron, finds himself duty-bound to flee his Doomed Hometown with Nuri in order to protect her even though, as his master explains to him just before his death, killing Nuri would stop the villain. She becomes Geron's Love Interest by the end as well. Being a fairy, Nuri has several magical abilities, though most of them cause her physical pain if she uses them. Dressed all in bright orange, and with feathers in her hair, she contrasts visually with most of the other characters in the game (who tend to wear neutral colors).
- Melissa in "Fortissima's Treasure Hunters". She was apparently encased in a large green crystal for several generations, is able to shoot fire from her fingers, speaks a backward language (literally! The words in her speech balloons are spelled in reverse), and her eyes glow when she sleeps.
- In many ways, Oasis from Sluggy Freelance is what you'd get if you trained her as an assassin and Brainwashed her into having a Yandere style crush.