Meet Bob. Bob is from a race consisting entirely of men (or they simply just look like men by human standards and don't actually have a concept of gender), but has always felt that something wasn't quite right about himself that he couldn't put his finger on. One day, Bob is sent out by his people to live among humans; during that time, he learns about their way of life, including their concept of gender. Eventually, she ends up transitioning to female and starts going by the name Barbara, making her the sole woman of a species that had no concept of womanhood before.
There can be multiple reasons why a creator might write a story like this rather than going for a straightforward transition story (male-to-female, female-to-male, either-to-nonbinary); nonbinary creators may use it to explore a Persecution Flip of their own experiences, trans creators of binary gender identities may use it to tell their stories while distancing themselves from their assigned sex at birth, and creators of all gender identities may utilize the contrast this one character has from their peers as a metaphor for the isolation one might feel being transgender in a cisnormative world. Then, of course, it may simply be for the mere speculation of how a sentient creature without our concept of gender identity would react to it or to evade any Moral Guardians who would oppose an explicit gender transition storyline.
To qualify for this trope, being The One Guy or the only female of their species is not enough; there has to be a confirmation of a change in gender presentation, especially if the character is the only one of their species shown. For examples where there are other members of the species, it has to be established that the target character's presentation is not the default and/or norm. Also, while human influence is a common catalyst for this kind of self-discovery, it is not a hard-set rule.
A subtrope of Speculative Fiction LGBT.
Examples:
- When IDW Publishing first started publishing Transformers comics as part of the eventual Hasbro Comic Universe, initially Cybertronians were introduced as a technically genderless species that used he/him pronouns for convenience. Arcee, the most famous female Transformer from the cartoons was said to be a victim of torture by Jhiaxus to force female gender identity on Arcee against Arcee's will including various mental blocks to make Arcee and others use she/her pronouns in reference to her. However, years later (and after female Transformers were reintroduced to the lore) under a different writing team, and having gotten feedback from LGBT fans about the representation issues involved, it was retconned in The Transformers Megaseries that Arcee was a trans Cybertronian with a female gender identity from birth and she had gone to Jhiaxus for gender confirmation surgery and whilst he had done so, he'd also tortured and experimented on her as well leaving her traumatized for a long time and only just coming to terms with the situation. Several original characters who also identified as transgender were added, as well.
- Discworld:
- Going Postal: The terrifyingly proper Ms. Maccalariat demands that something be done about the golem used as a janitor, as she deems it inappropriate to have the women's rooms cleaned by a non-woman (despite golems being sexless, genderless clay figures big and strong enough to rip a troll apart). The problem is apparently solved by giving the golem a dress, books on feminine etiquette and referring to her as Gladys, then turns into a different one in Making Money after Spike gives Gladys reading material that turns her into a Straw Feminist.
- Good Omens: Neil Gaiman has stated that angels and demons don't have an innate concept of "sex" or "gender" and picked up gender identities from mortals. In the 1990 novel, all angels and demons are referred to using male or female pronouns, but in Good Omens (2019), some are explicitly non-binary.
- How a Realist Hero Rebuilt the Kingdom: Dragons can shapeshift into humanoid forms. These forms are androgynous until and unless they form a bond with a humanoid Dragon Rider, at which time they'll take on either masculine or feminine forms in order to be the opposite sex from their rider, who is also their mate. It's noted that the logical consequence of this is that only dragons who bond with males are able to birth new dragons since humanoids cannot lay eggs.
- Looming Gaia: All nymphs have No Biological Sex, but they're referred to by she/her pronouns by default due to their feminine appearance. The only known exception to this is Austerity, a minervae who identifies as male and asked the divine Karenza to give him a masculine body.
- In The Moon Is a Harsh Mistress, the computer Mycroft is given a name by the male protagonist, who also keeps thinking of Mycroft as male. It takes his wife to realize that Mike isn't really male in any sense that he couldn't also be female in, which Mike — to the embarrassment of the protagonist — instantly agrees with. From then on, Mike takes up a secondary identity of Mychelle and casually switches between them depending on who is the other side in a given conversation.
- Star Wars: Per source books in the old Legends continuity, all members of the Hutt species are hermaphroditic and capable of asexual reproduction. However, many of them choose to identify as one gender or the other for the sake of convenience while interacting with non-Hutts.
- Topa from The Orville is an odd case; while she was born to an ostensibly all-male race that is capable of Homosexual Reproduction, biologically female Moclans do exist, though they are rare and treated as an aberration to be corrected with surgery and made male. This is what happened to Topa shortly after she hatched, and she spent the first year of her life living as a boy. However, when she learns about the surgery and is presented with the option to have it reversed, she accepts the offer and begins living as a girl from then on.
- Star Trek: The Next Generation:
- In the Season Three episode "The Offspring", Data builds a Soong-type android like himself, the titular offspring called "Lal". To Troi's surprise, the android body is androgynous and figured that Data would have made them human like he is. Data tells Troi that he wanted them to choose their own gender and appearance. Ultimately, after pairing it down to an Andorian female, a Klingon male, and a human male and female, Lal chooses the human female look.
- "The Outcast" introduces a genderless species called the J'naii whose evolutionary ancestors were a binary-sexed race and discriminate against the minority of their species who do still identify as male or female as they see this as primitive. A J'naii pilot called Soren identifies as female and falls in love with Commander Riker but the rest of her race find out and forcibly convert her through brainwashing to be agender again, much to Riker's horror. The episode was intended to be an analogy for discrimination against gay people but wound up being about gender identity and presentation instead.
- On 3rd Rock from the Sun, the aliens only had one gender in their original form, leading to much comedy when they attempt to understand human gender roles. While Sally initially wasn't happy with having to be the sole female of the Solomon family, she eventually comes to appreciate her new gender.
- Dungeons & Dragons:
- While the Warforged from the Eberron setting have No Biological Sex and thus usually don't pay the concept of gender much mind, some embrace a particular gender identity if they feel it suits them.
- Planescape: The 1997 sourcebook Faces of Evil: The Fiends states that Yugoloths are naturally hermaphroditic and any binary gender they express is a matter of personal choice. This was likely implemented due to a typo in 1996's Uncaged: Faces of Sigil where the Yugoloth crime lord Shemeshka the Marauder was referred to as female everywhere except her stat block, which had a male symbol, leading to speculation that she was a crossdresser or transgender.
- Monster Prom: Zoe is an Eldritch Abomination-turned-Cute Monster Girl who formerly went by the name Z'Gord and used it/its pronouns. The parallels to transgender experience are made even more obvious in her dedicated route, with her former cultists adjusting to the change much like parents would to their child's transition and Leonard continuing to call her Z'Gord being called out as transphobic.
- Final Fantasy XIV: Dragons are biologically genderless, but adopt gender identities regardless.
- Undertale: Ghosts, such as Napstablook, are genderless by default and use they/them pronouns. However, some ghosts take on binary gendered identities once they possess a physical body, such as Mettaton, who went from they/them to he/him, and Mad Mew Mew (formerly known as the Mad Dummy), who went from they/them to she/her.
- In Magical Boy, the finale of the comic reveals that Aurora and Devoid were originally genderless beings before choosing their genders in emulation of the beings they wished to be like. Aurora admired female organisms' ability to create life, becoming a goddess, while Devoid became worshiped as a "king" despite also identifying as female. This is why Devoid is referred to with male pronouns in the present because of the masculine associations of the title "King of Darkness".
- Runaway to the Stars: Shyam is a member of a hermaphroditic Human Subspecies who identifies as female rather than non-binary like most of her clade.
