Mahiro's Big Secret (Part 1)

Mahiro's Big Secret (Part 1) (まひろと大事なヒミツ（前編）, Mahiro To Daiji Na Himitsu (Zenpen)) is Chapter 39 of Onimai: I'm Now Your Sister!. It was originally published on Pixiv on April 25, 2020.

Summary
Mahiro and her friends begin a new school year, and meet someone new in the process.

Plot
Mahiro puts on her school uniform to get ready for school. As she fluffy her hair in the mirror, she has mixed feeling about a new school year beginning so soon.

Mihari starts letting out tears, and Mahiro asks what's wrong with her. Mihari says that she is amazed that Mahiro is getting herself ready for school without even pitching a fit, noting that Mahiro has really grown a lot. She remarks that this must be how every proud mother feels, with Mahiro calling her out on the fact that she's not even considered her sister now. Mihari waves Mahiro out the door, telling her not to talk to any suspicious characters. Mahiro leaves while thinking about what Mihari means, as she's the only suspicious character that she knows.

As Mahiro walks to school, she notes that time really has flown by and that she shouldn't be so careless about this. She realizes that if she doesn't do something soon she'll be a high school girl before too long. Her heart races while imaging herself in a high school uniform, along with an older Momiji who has grown out her hair. Mahiro realizes that maybe there's a bit of wishful thinking in there too.

Momiji sees Mahiro and wishes her a good morning, Mahiro does the same to her. Mahiro notices that Momiji has put her hair back in her signature topknot, and Momiji says that she did that because it's getting warmer now, Kaede remarks that it looks much cuter down, like a kokeshi doll. Momiji in response suggests that Kaede goes back to her older hairstyle so they can match, an idea that Kaede quickly shoots down causing Mahiro to laugh. As the two hug and make up, Mahiro thinks to herself that letting things stand a little longer isn't so bad.

Momiji says that she is worried though, and Mahiro asks her what it is that she's worried about. Momiji points out that a new school year means new class assignments, and that she is worried that they all might get split up into different classes or something. Mahiro becomes worried as fell, having completely forgotten, knowing that one little change might cause the whole status quo to come crumbling down. Mahiro hugs Momiji, begging her to remain her friend even if they get split up. Momiji is confused, but agrees. Kaede giggles at the youth of Mahiro and Momiji.

In Class 2-B, Asahi is overjoyed that everyone managed to remain together and hugs Mahiro and Momiji's heads. Momiji tells Asahi to get off while Miyo laughs at the situation.

Mahiro sighs in relief, noting that she recognizes a lot of the other kids as well. She notes that she thinks she can live with this and is happy that things are still the same. A girl bumps into Mahiro, leading Mahiro to apologize. As the girl takes her seat, Mahiro realizes that she is a new face that she doesn't know.

Asahi beams over Momiji's topknot returning, leading Momiji to sigh over the face that Asahi just noticed. Asahi begins playing with it, noting that it's just the way it should be. In response, Momiji tells Asahi to not mess with it.

Momiji asks Mahiro what hairstyles she prefers. Mahiro struggles to come up with an answer for a few seconds, wondering why Momiji had to ask her something so difficult. Mahiro eventually says that she thinks that one's hairstyle should reflect their personality and identity, as hair that unmistakably you is best of all. The three girls are amazed at that answer, and Momiji remarks to Mahiro that she sounds so mature sometimes. Miyo agrees, and Mahiro thinks to herself the she agrees with the "sometimes" part. The girl from earlier watches this exchange and smiles.

Mari comes in and tells everyone that it is time for the year-opening assembly. She tells them all to line up as they're going to the auditorium, and everyone agrees.

In the auditorium, the principal tells the assembled students to let this be a new beginning for all of them. Mahiro notes that assemblies are always so long, not that she expected anything else. This time however, she really has to pee. She notes that she isn't the shy maiden she used to be, and decides to ask Mari if she can go if things get too desperate. She notes that it's not like Mari's going to say no, thinking that they're talking a human rights violation if she does. She also realizes that if she sneaks out quietly it won't disturb anyone. Asahi notices Mahiro struggling and announces to Mari (and everyone in the vicinity) that Mahiro needs to use the restroom. Mahiro is surprised and embarrassed, especially as Mari giggles a bit while Asahi gives Mahiro a thumbs up. Mahiro decides to accept it, deciding that anything is better than peeing herself, and races to the bathroom.

In the end, Mahiro doesn't make it despite making it within sight of it. Despite her predicament, she feels no embarrassment, instead thinking that she think's she'd be used to her new body's limits by now. A voice calls out to Mahiro saying that she's in a real pickle, causing Mahiro to jump. Mahiro realizes that it's the girl she bumped into in class, and the girl tells Mahiro to call her Nayuta, also explaining that she snuck out of the assembly as well. Nayuta suggests that they go to the Nurse's Office for now, adding that no one's there but they can get Mahiro a change of underwear. Mahiro, somewhat embarrassed, agrees.

In the Nurse's Office, Mahiro sits on a a bed wearing her replacement underwear and sighs. She notes that this really was a first impression, making someone she just met clean up her mess. Nayuta opens the curtains and asks if they fit okay, and Mahiro notes that they fit fine. Nayuta looks closer at Mahiro and tells her that it was a nice job keeping her uniform dry, saying that she must be a master hand at this. Mahiro feels embarrased and tells Nayuta not to call her that.

Nayuta tells Mahiro not to worry and says that she'll keep her secret, saying that her mouth is like an iron trap. Mahiro smiles and thanks her. Nayuta then says that, of course, she also knows Mahiro's other secret. She asks Mahiro if she's right, calling her "my pretty little onii-san", much to Mahiro's shock and confusion.

It is revealed that as Mahiro ran from the assembly, Yuta and Minato both realized that she had to pee.

Characters

 * Mahiro Oyama
 * Mihari Oyama
 * Kaede Hozuki
 * Momiji Hozuki
 * Asahi Ōka
 * Miyo Murosaki
 * Nayuta Tenkawa
 * Nemu Fujimi
 * Nodoka Fushimi
 * Aoi Tachikawa
 * Yuta Sakurada
 * Minato Senkawa
 * Mai Yasaka
 * Miyako Nagase
 * Mari Nishinomiya
 * Rin Minakata

Trivia

 * First appearance of Nayuta Tenkawa.
 * Momiji once again wears her topknot starting with this chapter, having worn her hair down to keep herself warm during winter since "Mahiro and the Allure of Bare Legs".
 * Kaede indirectly references when Mahiro thought that Momiji's spirit animal was a kokeshi doll in "Mahiro and the Guidance of the Stars".
 * This is the first chapter where Mahiro and her classmates are second year middle school students and members of Class 2-B.
 * This marks the first time that Mahiro wets herself and doesn't feel embarrassed about it.