William Shakespeare: And thus is unable to declare her love.
Viola: But all ends well.
Our protagonist is a stranger trapped in a strange land. They need to infiltrate the social fabrics for one reason or another. Often, this reason is survival. Problem is, their true gender, if noticed, wouldn't allow them to blend in. Maybe they would be stuck in a ghetto or cage or breeding farm. Maybe they would be expelled. Maybe they would be killed... This could be because of a Lady Land or No Woman's Land.
But our protagonist does what they have to and becomes a Wholesome Crossdresser who will attempt to integrate themselves into the setting. How well, and for how long, is what drives the plot.
As a rule, the establishment is draconian and ironclad in its traditions, and is more often than not militantly hateful towards the gender it excludes. Through their sensitivity, kindness and unique "outsider" perspective, our protagonist will (usually) challenge the preconceived and narrow perceptions of their fellow cast members...
...and with a little bit of luck, change the establishment into one of kindness and tolerance by the time their true gender is exposed.
Note if you're a Japanese character on this adventure, you'll more often than not fall victim to the Gender Vocabulary Slip, as Japanese is a language with very gender-specific first-person pronouns. See Different for Girls for other shenanigans related to that.
Compare Sweet Polly Oliver.
- Ouran High School Host Club, in which our heroine Haruhi is talked into joining the club and masquerading as a wholesomely sweet boy to cater to their female clientele. It deviates from the usual formula in that her clubmates, at least, are fully aware of the ruse and it's not really Haruhi (who simply has boyish tastes in clothing and hairstyle, and is entirely indifferent to what sex people think she is) trying to maintain the masquerade, but everybody around her.
- I My Me! Strawberry Eggs started out as this, with the Hot-Blooded young teacher trying to prove the tyrannical Straw Feminist organisation's disdain of men wrong... only to fail bitterly. It turns out he's not the only one doing it, though.
- Otoboku - Maidens Are Falling For Me is one of the funniest and most heartwarming examples in anime, wherein kind-hearted Wholesome Crossdresser Miyanokouji Mizuho becomes the most beloved "Onee-sama" and a pillar of strength of his circle of friends in a Catholic Girl's School.
- In MariaHolic, the crossdresser in question is actually not the main character. He is also apparently a cruel person who cares not one whit about other people.
- In the first OVA of El-Hazard: The Magnificent World, after finding himself in another dimension, the main character Makoto is forced to crossdress in order to pose as the missing princess Fatora.
- The manga series Girl Got Game is about a high school girl named Kyo Aizawa who disguises herself as a boy in order to join Seisyu High's famous men's basektball team. However, it was her father's idea; she'd rather go to a normal school as a normal girl.
- The manga series Mint na Bokura is about a boy whose twin sister transfers to a boarding school to be closer to the boy she has a crush on. He transfers to the same school because he doesn't want to be separated from her, but there's a catch: the boys' dorm is full, so he has to disguise himself as a girl and live in the girls' dorm.
- In Hana-Kimi, a Japanese-American girl wanted so much to meet her idol she decided to enroll the same school he attends. The problem is that he attends an all-boys school. He soon found out and started to like her. The plot point is that he doesn't know she likes him and she thinks he still doesn't know she's a girl. When rumours start to abound of a girl on campus and her facade starts to crack via various Bridget-droppings, she decides to transfer to a public school while the going's still good, though she and her idol meet up again in college and become an item in the epilogue.
- The manga series AKB49 Renai Kinshi Jourei is about an Ordinary High-School Student cross-dressing to join an all-girl idol group so that he could secretly protect his crush, who is also in the same group.
- In Marugoto Anju Gakuen, our protagonist is pretty much forced to join an all-girl academy for yokais by his mother.
- Futari wa Pretty Cure Dragon has a male protagonist who winds up accidentally enrolling in a girls' school because he was trying too hard to pass an entrance exam after failing so many. The other protagonist is a girl through and through, and she finds out in the first episode right before they become the titular magical warriors.
- The truly squick-tacular Wayan Brothers film White Chicks has two black male police officers masquerade as weirdly plastic-looking white valley-girls.
- Amanda Bynes in She's the Man (which is a Setting Update of Twelfth Night) infiltrates an all boy's soccer team to prove that girls can play soccer just as well.
- And two decades earlier, a girl infiltrates another high school's senior class as a boy to try to prove gender bias in her school's newspaper in Just One of the Guys. The fact that her name was Terry didn't hurt. The funny part is, she failed miserably — turns out her writing to start with wasn't very good — but the Twelfth Night plot helped her to improve.
- Disney's Mulan. This trope actually gave the family film some unexpected and refreshing parental bonuses.
- Although one does notice that the character is drawn differently when she pretends to be a man. Look at the movie poster where half of her face is reflected in a sword. Notice her nose and jaw.
- And apparently her eyebrows grew in no time.
- Notice that this is based on an old Chinese poem "Poem of Mulan", making it older than Shakespeare.
- Dustin Hoffman in Tootsie.
- Yentl had this, as it was set during a time when women were not to become educated.
- Robin Williams as Mrs. Doubtfire is another example, where a failed actor must pass as a woman to be hired as a nanny to tend to his own estranged children.
- Some Like It Hot is a classic example that has the two male protagonists forced into this trope to go incognito and lose the mobsters looking for them.
- Nuns on the Run: Two crooks steal loot from one set of gangsters, who stole it from another, and then there's the police to worry about as well. Their only chance of surviving is trying to pass unnoticed in a nunnery, which means becoming nuns. (The film later forces them to pose as nurses and air hostesses as well).
- Tamora Pierce's Song of the Lioness series starts as a more dramatic example of this plot with Alanna becoming a Sweet Polly Oliver so she can become a knight, though her gender gets revealed at roughly the halfway mark.
- The male protagonist of A Planet Called Treason develops breasts due to a genetic disorder and parleys it into the opportunity to infiltrate an all-female society.
- All Men of Genius is about a woman who wants to attend a prestigious scientific academy which only accepts men, and who impersonates her brother to get there. It contains many explicit nods to Twelfth Night (the main character being named Violet, the school being called Illyria, etc.)
- Twelfth Night by Master William Shakespeare, obviously, created this Older Than Steam genre and named this trope.
- In Princess Ida by Gilbert and Sullivan, Hilarion, Cyril, and Florian disguise themselves as women to infiltrate the women's only school where Ida teaches women to not like men. Turns out, once the women get to know the men, they find them pretty likeable after all.
- In Random Encounter, Princess Paige comes to DHS seeking, specifically, a male escort due to "tradition." The school, not thinking any faculty up to the task, and not wanting to risk the lives of mortal students, dresses Claw up as a boy and sends her. Paige's entourage fail to mention that the "tradition" entails reenacting the journey of Reis and Hind, which ended in their marriage. As a consequence, Claw, aka Prince Phoenix, her and Paige having decided to stay together after clearing the air, may be trapped in her adventure for a long time.