Maomarimo is a short seinen manga written by Aoi Horikata and illustrated by Shiki Tanisawa. It ran in Young Animal from 2010 to 2011.
Like most rural Japanese villages, Tamano celebrates an annual festival in honor of its own own local deity, the Marimo (seaweed ball) guardian spirit. But unlike most such communities, the Marimo festival includes a Virgin Sacrifice. Nothing bloody or horrific, mind: It's a purely symbolic sacrifice that involves dressing a local maiden in ceremonial robes and making her spend the night in a boat out on the lake. No muss, no fuss, no blood, and so far, no casualties.
Unfortunately, this year there's a problem. This year's sacrificial maiden, Akoya Nota (Ako to her friends) is prone to seasickness and hates boats. So her beloved twin brother Mao decides he'll go in her stead and protect his more outgoing sister just as Ako has always protected him. Mao dons the robes and boards the boat while Ako is distracted. They may not look anything alike but they're about the same size and in the robes and the dark who's to know? Well, apparently the God knows, because there's a loud booming sound followed by a dense fog, and when the boat drifts back to shore the next morning, Mao's been turned into a girl!
- A-Cup Angst: Ako, but only after she learns that her "brother" needs a larger bra size than she does.
- Always Identical Twins: Invoked by one of Mao and Akoya's classmates, who wonders why the two aren't more alike now that Mao is a girl too.
- Big Sister Instinct: Ako has always protected Mao...except this once, and the guilt is tearing her apart.
- Big Eater: Ako
- BrotherSister Incest: Ako's interest in Mao wasn't entirely healthy, but it apparently wasn't acted upon or reciprocated either, as Mao has no clue.
- Contrived Coincidence: Ako and Mao are born the same day despite not being real twins, which let Mao take Ako's place in the festival.
- Dangerous 16th Birthday: The festival takes place on Ako and Mao's 16th birthday, most likely being scheduled on that date specifically because of the former.
- Decoy Protagonist: Despite the title, the story so far has been more about Ako's and Jiu's reaction to Mao's change than Mao's.
- Different for Girls: Unusually, the work is primarily focused on how things are different for everyone else (mostly Akoya) now that Mao is a girl. Ako is less than thrilled to help Mao learn feminine deportment because she doesn't want Mao to be a girl at all.
- Disappeared Dad: working overseas, apparently
- Gender Bender: Mao takes his sister's place in a holy ritual meant for a young woman, and the god responds by actually making him a girl.
- Gender Bender Angst: Played with. Mao appears to have accepted her Gender Bender, it's Ako and Jiu who continue to object. Ako because she's wracked with guilt and Jiu because he thinks it's a travesty that no one appears interested in curing his best friend. However, Mao's inner monologue reveals that she's not as complacent as she appears, just trying to put the best face on things.
- Feminine Women Can Cook: Mao is an excellent cook and Ako is a Lethal Chef
- The Ingenue: both Mao and her eldest sister Sakura
- Jumping the Gender Barrier: Mao's best friend Jiu is not prepared for his own reaction to his newly feminized friend
- Masculine Girl, Feminine Boy
- Missing Mom: died at some point in the past.
- Not Blood Siblings: Mao and the girls, though Mao doesn't know and her sisters only found out from their father's letter on the night of the festival after Mao boarded the boat.
- Polar Opposite Twins
- Shower of Angst: Ako. Between her illicit feelings for Mao, the belated reveal that she could have acted upon them as Mao wasn't really her brother (something she's still keeping secret) and her conviction that Mao is being punished for her transgression the poor girl has a lot to feel guilty about.
- Smoking Is Cool: Inverted. Mao tells Jiu his smoking just makes him look more like a kid, especially since he doesn't inhale.
- Sweet Tooth: Mao wants to be a pastry chef.
- Third Law of Gender-Bending: Mao pretty much jumps into girlhood with both feet, and the whole village seems willing to oblige because they want to protect everyone involved from public embarrassment. Even Ako is torn on this point. She wants Mao to go to Tokyo for medical treatment (and presumably a cure) but is afraid of what the inevitable publicity would do to Mao.
- Tomboy and Girly Girl: Ako and Mao. Just another thing that makes Ako uncomfortable, because Mao seems determined to become as girly as possible as soon as possible because she thinks it will help her get used to the change.
- Transformation Comic
- Tsundere: Ako
- Twin Switch only once. Once is enough.
- Virgin Sacrifice: The village elder speculates that perhaps the true, original form of the "maiden sacrifice" is a boy sacrificing his manhood to become a maiden. You have to admit an involuntary sex change is a much bigger sacrifice than a boat ride.
- Wide-Eyed Idealist: Mao again. How much of this is an act is not clear.