Mahiro Oyama

Mahiro Oyama (, Oyama Mahiro) is a former otaku slacker and the brother-turned-sister of Mihari Oyama, having been transformed into a middle-school aged girl by one of Mihari's experiments. She is voiced by Marika Kōno in the anime.

Appearance
Mahiro's appearance as a guy directly before the transformation has never been fully seen. As a kid, his face looked surprisingly similar to how it currently is, but with his pinkish-gray hair being much shorter.

After being transformed into a middle-school aged girl by Mihari, Mahiro's hair now stretches to the middle of her back with a single strand on the top poking up and two longer stands that fall to the front and cover her ears. She is also now slightly smaller than Mihari and gives off the appearance of an extremely cute and adorable young girl. Due to Mihari having replaced all her male clothes, Mahiro is now seen wearing skirts and dresses almost exclusively. Despite this, she rejoices whenever she gets the chance to wear what can be considered boyish-clothing.

As time goes on, Mahiro starts to mature both physically and emotionally. While still cute, her outfits begin to strike a more mature cord through the use of tights and jackets. She grows slightly taller and her bust size also increases allowing her to upgrade to standard bras.

Personality
Mahiro used to be a degenerate slacker with a love only for manga with stories of bondage and sex slavery, and staying home playing video games. It was noted that before the start of the series, he hadn't left his house for two years. According to Mihari, Mahiro wasn't always like this.

When they were younger they were very close and got along famously. Mahiro would buy his sister stickers when she asked for them, won her stuffed animals at amusement park games, and even gave her her signature hair clip as a reward for doing well on a test. He stopped making time for her as he got older and her achievements surpassed anything he could ever hope to achieve, as the result of a combination of an inferiority complex next to Mihari coupled with adolescent pressure. Despite this, Mahiro has shown an inherent talent for composing haikus about her everyday life.

After being transformed into a girl by Mihari, Mahiro didn't put up much of a fight, though she did show some initial resistance to going outside, showering regularly, and putting up with all of Mihari's new rules for her. As time went on, her old personality started to fade away and she started exhibiting the personality of an adorable younger sister who loved dressing up and being taken care of by Mihari. The main aspect of her old personality that remained however was her love for video games, and she is seen playing them constantly in her spare time. Overall, the roles of Mahiro and Mihari have since reversed with Mihari taking care of Mahiro rather than the other way around.

At the start of the series, Mahiro hated going outside and felt overwhelmed by large crowds due to spending two years inside her house as a shut-in. Spending time with Kaede and Momiji helped to lessen the discomfort and it eventually disappeared shortly after she was enrolled in middle school. Although it still pops up from time to time, Mahiro gets through it by hanging out with her friends.

After being hit on the head by a box, temporarily losing her memory, and gaining the personality of a little girl in the process, some of this other personality has begun to leak through on occasion. This is shown by actions such as the occasional cutesy expression, taking naps after eating cookies much to Mihari's frustration, and feeling uneasy about the sex-slavery and bondage X-rated manga that she used to devour.

A running gag throughout the series is Mahiro wetting herself due to not reaching the toilet in time, but also due to an occasional fright. Miraculously, during these incidents she is able to keep her dresses or skirts from getting wet, and only her underwear and tights takes the blow. She originally felt extremely unhappy and embarrassed when it happened, but it has happened so often now that she's gotten used to it and it doesn't bother her anymore. This self-confidence has even helped Momiji feel better when she also suffers from similar incidents.

Mahiro, despite being female now, is still shown to be nervous and slightly aroused by being in close contact with girls, especially those who are undressing. She loves seeing Kaede show off her body in a swimsuit, and loved how Asahi smelled while she pulled Mahiro's head into her chest for a hug. Mahiro knows that she would look weird while doing this, so while changing with other girls she tends to look at those of her friends that are flat chested to calm herself down, comparing it to looking at "the desolate beauty of the great plains". This, however, makes her look weird anyway by those she is staring at.

Despite multiple occasions where the drug has started to wear off (causing Mahiro's "comrade" to regrow), Mahiro has opted to continue taking additional doses of the drug to remain female. She continues to assert her lost masculinity and rejoices when her "comrade" returns, but has opted to stay female for the time being due to loving all her new friends and her new life. She has ultimately opted for trying to find a balance between her old life and new one.

Mihari Oyama
When they were younger, Mahiro got along famously with Mihari. They would play together, and tease each other as brothers and sisters often do, but they also deeply cared about one another and Mahiro would do his best to take care of her as her older brother. This started to change after it became apparent that Mihari was a prodigy whose achievements began to surpass anything that Mahiro could ever hope to achieve. As a result, he stopped making time for Mihari and became isolating himself in his room, sleeping in past noon and playing video games while never leaving the house for a period of two years before the start of the series.

Despite Mahiro no longer caring what Mihari did, she did still care about her older brother and began an experiment to completely rehabilitate his life and make him a functioning member of society through her "Onii-chan Rehabilitation Project" which involves transforming him into a middle-school aged girl and slowly making her a functional member of society by giving her a new life as Mihari's younger sister. She thus takes pleasure in observing how the experiment is progressing, seeing Mahiro as a lab-rat for it.

Since Mihari transformed him into a middle-school aged girl, their relationship has reversed with Mihari now taking care of Mahiro. Mihari always wanted to have a younger sister, and is now taking advantage of the experiment to live out her long sought after fantasies. This is shown by her dressing Mahiro up in various girly outfits, and baking cookies for her. She also gets extremely excited whenever Mahiro acts cute and feminine, though she does get frustrated when Mahiro starts acting more feminine than she does (and tends to point it out). When Mahiro does something nice for her, or when Mahiro puts in a lot of hard work into something and fails, she bursts into tears showing how much she truly loves her and what she does.

Mahiro in turn adores her older sister now, and the two have become closer and closer, though she is occasionally inconsiderate, especially when distracted by the video games she plays.

Kaede Hozuki
When they first met, Mahiro was worried that Kaede would know who she really was, but the two started talking and found that they enjoyed each other's company. As a result, Kaede has become another big sister figure in Mahiro's new life. Kaede is always willing to help out Mahiro if she asks for it, and the two have even started keeping secrets behind Mihari's back. Kaede has even helped Mahiro and her friends cook, bake, and pick out new swimsuits.

Momiji Hozuki
When Mahiro first met Momiji, Momiji was dressed in such boyish clothing that Mahiro thought that she was a boy. A connection was formed between them almost immediately, though Mahiro started to get worried about her flustered feelings towards Momiji after someone remarked that they looked like a couple. Mahiro was amazed when she learned that Kaede was Momiji's older sister. She was also shocked, and at the same time relieved, when she realized that Momiji was actually a girl. She was delighted to be called Momiji's friend, and the two looked forward to seeing each other again.

A few weeks later, Mahiro met up with Momiji again when Momiji came to her house with Kaede. Mahiro at first didn't recognize her due to her wearing a skirt that day, but was delighted to see her again once things were cleared up. Mahiro tried to make her room presentable when Momiji come into it, and they subsequently struck up conversations on the merits and drawbacks of wearing skirts. Momiji was shocked to find Mahiro with X-rated hentai manga, but Mahiro cleared it up by claiming that it belonged to her [nonexistent] older brother who was away at college (with this originally having been his room). After they boxed up the manga, an incident caused Momiji to land on top of Mahiro and grope her bust with both hands, much to both of their embarrassment. Despite this, the two still enjoyed each others company and decided to remain friends.

Following a few more incidents where Mahiro visited on Halloween, and Momiji almost discovered that Mahiro was a boy on a trip to a hot spring, the two grew closer and closer. Eventually, Momiji invited Mahiro out to meet her two friends Asahi and Miyo, and the four all became close friends.

Momiji is shown to be very jealous when Mahiro pays any intimate attention to anyone other than her, and this has led her to be strangely competitive with others for Mahiro's attention (particularly with Asahi). When Asahi offered Mahiro a bite of her parfait, Momiji ate it herself and then forcibly fed Mahiro a bite of hers, getting into a battle with Asahi over whose was better. She repeated this when Mahiro offered Miyo a bite of her crepe, force feeling Mahiro a bite of hers. Mahiro noted that Momiji's spirit animal could be the bear since she's so soft-hearted and reliable, but Asahi pointed out that it could also work since she tends to get weirdly aggressive at times (which Momiji ironically proved when she slammed Asahi's head into her desk for saying that).

Momiji is the only one in the group (out of her, Asahi, and Momiji) who's come close to finding out that Mahiro was really a boy. She groped Mahiro's "comrade" by accident while in the hot spring, and immediately became suspicious when Mahiro raced out of the spring. Later that night, she decided to look for herself, but saw nothing as it had disappeared as a result of the new dosage of the feminization drug. That morning, seeing Mahiro react girlishly to a perm given by Kaede put her worries to rest, permanently.

Ultimately, Momiji is considered Mahiro's best friend, and is the one that Mahiro hangs out with most often outside their circle of friends.

Asahi Ōka
When Mahiro first met Asahi, she was nervous about going out with two new strangers. Asahi came off as inconsiderate by being brutally honest about what Momiji said about her, but it broke the ice and caused Mahiro to laugh in relief as she no longer had to pretend to be someone she wasn't. Mahiro was relieved and quickly accepted Asahi as a friend.

Mahiro and Asahi are polar opposites in almost every way. Asahi is energetic, adventurous, extremely athletic, and speaks her mind, while Mahiro is subdued, more of a shut-in, lacks strength and stamina, and thinks out what she says. Despite this, the two share a very good relationship. Mahiro adores how honest Asahi is with her feelings, such as telling Mahiro to talk about her games since she looks so happy when doing so. Mahiro in turn sees Asahi almost like a pet, with her regularly rubbing her hair and calling her a good girl while doing so. When it comes to adventures, Asahi tends to drag Mahiro along for the ride. Due to Mahiro's lack of stamina, she gets tired very quickly, though Asahi is still happy to have her along.

Mahiro also enjoys Asahi's innocence, and notes the irony of many things she tends to say that go over her head as a result, which Mahiro is entertained by.

Miyo Murosaki
When Mahiro first met Miyo, she was nervous about going out with two new strangers. She was a bit confused by Miyo's Yuri shipping of her and Momiji, but quickly caught on and accepted it as a part of who she was. The two subsequently became good friends.

Mahiro got closer to Miyo when she ran into her in disguise trying to buy Yuri manga at Tachikawa bookstore. She agreed to keep the fact that Miyo was into Yuri a secret (despite the fact that it was already well known), and encouraged Miyo not to be embarrassed of what she enjoys. Miyo has since offered Mahiro a glimpse into Yuri by recommending several issues of titles she enjoys, which Mahiro has come to enjoy.

Mahiro is a bit confused as to why Miyo is so embarrassed about being so well developed, but hasn't pushed the issue. Also, similar to the others, Mahiro is a bit put off by Miyo's idea of romance when it comes to girl talk, though she is thankful that Miyo is so level-headed compared to Momiji and Asahi.

Etymology

 * The characters for her first name, Mahiro (真尋), literally mean "true" (真) (ma) and "fathom" (尋) (hiro). The author, Nekotofu, has noted that he gave this character this name because it is unisex (i.e. there are both men and women named "Mahiro") and shares the same consonants with her sister's name, Mihari.
 * The characters for her last name, Oyama (緒山), literally mean "string" (緒) (o) and "mountain" (山) (yama). According to Nekotofu, the name comes from oyama, a term in kabuki that refers to male actors who play female roles.

Trivia

 * In the original Japanese version, Mahiro refers to herself as オレ (ore), a common first-person pronoun which sounds masculine and informal, sometimes rude or crude depending on the context, but she does so only when she is by herself or alone with Mihari or Nayuta, both of who know that she is actually male. In other situations, Mahiro is more inclined to use わたし (watashi) instead, a pronoun which is feminine or gender-neutral.
 * Although it is revealed that the kanji for her first name is "真尋", her name is almost always written in hiragana, like "まひろ".

Manga

 * Mahiro's Confusing New Body
 * Mahiro and the Bathroom
 * Mahiro Faces the Mirror
 * Mahiro's Self Image
 * Mahiro Plays an MMO
 * Mahiro's Melancholy Day
 * Mahiro, Even on Heavy Days
 * Mahiro and the Secret Garden
 * Mihari's Wasted Efforts
 * Mahiro's Unexpected Encounter
 * Mahiro Starts Over
 * Mahiro and the Gatcha Game
 * Mahiro and the Girls' Day Out
 * Mahiro and Kaede's Secret
 * Mahiro the Own-Home Security Guard
 * Mahiro Helps Out
 * Mihari and Her Onii-Chan
 * Mahiro Falls in Love
 * Mahiro's Night Alone
 * Mahiro's Sunday Morning
 * Mahiro's Wholesome Playdate
 * Mahiro's Little Adventure
 * Mahiro Attends a Party
 * Siblings Share the Kotatsu
 * Mahiro Visits the Salon
 * Mahiro's Panic! At the Hot Spring (Part 1)
 * Mahiro's Panic! At the Hot Spring (Part 2)
 * Mahiro and the Comrade's Return
 * Mahiro's Perm
 * Mahiro the Streamer
 * Mahiro and the Middle Schoolers
 * Mihari's Wardrobe
 * Mahiro's First Day
 * Miyo's Refusal
 * Momiji's Nickname
 * Kaede's Concern
 * Mahiro's Difficult Class
 * Mahiro's Exciting Weekend
 * Mahiro and Conversation
 * Mahiro's Lunch
 * Mihari's Lunch
 * Mahiro's Final Exams
 * Mahiro's Touch
 * Asahi's Innocence
 * Mahiro the Patissier
 * Mahiro's Twisted Logic
 * Mahiro's Sleepover (Part 1)
 * Mahiro's Sibling Bathtime
 * Mahiro's Sleepover (Part 2)
 * Mahiro's Double Date
 * Mahiro Rings in the New Year
 * Mahiro and the Spicy Kiss
 * Asahi and Momiji
 * Mahiro and the Allure of Bare Legs
 * Mahiro and the Unexpected Guests
 * Mahiro and the Mystery Brew
 * Mahiro on Valentine's Day
 * Mahiro and the Homemade Chocolate
 * Mahiro and the Adult's Only Section
 * Asahi's Crepe
 * Mahiro's Yuri Manga
 * Mahiro's "Something"
 * Mahiro and the Guidance of the Stars
 * Mahiro's Surprise Party
 * Mahiro's Final Present
 * Mahiro Pretties Up
 * Mihari and the High School Girls
 * Mahiro's Relaxing Day Off
 * Mahiro's Big Secret (Part 1)
 * Mahiro's Big Secret (Part 2)
 * Mahiro's Bare Feet
 * Mihari's Skipped Grades
 * Mahiro and the School Physical
 * Mahiro and the Health Committee
 * Mahiro and the Spankies
 * Mahiro and the Gifted Experience
 * Mihari and the Stuffed Animal
 * Mahiro and the Perfume
 * Mahiro and the Full-Cup Bra
 * Mahiro and the Barbecue Secret
 * Mahiro and the Seasonal Attire
 * Mahiro and the Sticker Collection
 * Mihari's Sticker Memories
 * Mahiro and the Sunshine Girl
 * Kaede's Nickname
 * Mahiro and Visitation Day
 * Mahiro and the Parent-Teacher Conference
 * Mahiro and Swim Class (Part 1)
 * Mahiro and Swim Class (Part 2)
 * Mahiro and the Comrade's Return Again
 * Nayuta's Recent Past
 * Mahiro's Colorful Life
 * Mahiro and the Rainy Season
 * Mahiro and Self-Styling
 * Mahiro and the Little Garden
 * Mahiro, the Sun, and the Northern Wind
 * Girls and Boys
 * Mahiro and the After-School Fright
 * Mahiro's Cool Head
 * Mahiro and the Midsummer Romance
 * Mahiro and the Strategy Meeting
 * Kaede and the Junior High Girls
 * Mahiro's Beach Fun (Part 1)
 * Mahiro's Beach Fun (Part 2)
 * Mahiro and the Squishy Thingie
 * Mahiro's Deep Clean
 * Mahiro's Summer Homework
 * Mahiro and the Photo Albums
 * Mahiro's Anime Time
 * Mahiro and the Summer Festival
 * Mahiro's Second Semester Debut
 * Mahiro Shelters From the Storm
 * Momiji's Panty Problem
 * Mahiro's Weight-Loss Plan
 * Mahiro and the Charming School Festival (Part 1)
 * Mahiro and the Charming School Festival (Part 2)
 * The Boys' Shift Change
 * Mahiro's Masculine Ego
 * Mahiro and the Safety Pants
 * 2020 Summer Special Brochure
 * Mahiro and the Fan World
 * Mahiro's Field Day
 * Mahiro's Cheer Wear
 * Mahiro's Autumn Outing
 * Mahiro's Cosplay Round-Table

Anime

 * Mahiro's Confusing New Body
 * Mahiro's Time of the Month
 * Mahiro's Close Encounter
 * Mahiro's New Friend
 * Mahiro Discovers Adventure and Social Gatherings
 * Mahiro Goes Back to Middle School
 * Mahiro's Role-Playing Game
 * Mahiro's First Girls Sleepover
 * Mahiro Rings in the New Year
 * Mahiro Ponders Boobs and Identity
 * Mahiro Pretties Up
 * Mahiro's Future as a Sister