Mahiro's First Day

Mahiro's First Day (まひろと初登校, Mahiro To Hatsutoukou) is Chapter 21 of Onimai: I'm Now Your Sister!. It was originally published on Pixiv on October 28, 2018.

Summary
Mihari enrolls Mahiro in a nearby middle school, where she is placed in the same class as Momiji, Asahi, and Miyo.

Plot
Mihari, following on her previous suggestion of Mahiro going to school, enrolls Mahiro back in middle school.

On her first day, Mahiro introduces herself in front of the class, which is revealed to also contain Momiji, Asahi, and Miyo who are happy to see her. As the teacher Mari tries to find a spot for Mahiro, Mahiro panics thinking to herself that she can't do this.

Earlier that morning, Mihari is shown telling Mahiro that it is time for school. Mahiro cowers behind a door saying that she can't, and won't. She calls Mihari a fiend, saying that trying to force a defenseless "own-home security guard" like herself to do this is child abuse. Mihari is surprised at that statement, and asks Mahiro if it's boring for her to be cramped up in the house all day. Mahiro claims that it's great, calling keeping her XP gains maxed out is a lot of work. Mihari says that she'd rather Mahiro gain experience in the real world instead of a game. Mahiro asks about the paperwork, and Mihari chuckles, saying that she has her ways. Mahiro gets a feeling of dread and wonders whatever happened to her sweet little sister.

Mihari further explains that she has taken care of it, saying that she has a cover history prepped and everything, and that it's all accounted for. Mihari asks Mahiro if she can go once just for fun. She even promises Mahiro that she won't need to study or anything, and that in the worst case scenario she could just stop going. She starts hugging Mahiro from behind asking her to do it for her, much to Mahiro's protest. Mihari adds that all of Mahiro's new friends will be there as well, but this does little to lift Mahiro's spirits.

Back in the present, Mahiro has taken her seat and thinks to herself that she really should've put her foot down on this. She cannot believe that she is actually repeating middle school of all things, and this time as a girl.

As she thinks this, Mahiro is surrounded by her new classmates who want to get to know her better. They start saying things like "Good morning", "You're cute", "Such pretty hair", and "Where are you from?". Mahiro knows that it is the trial that every transfer student must face, but struggles to get out a response.

Another classmate tells them all to back off a bit, saying that if they badger Mahiro all at once she'll get overwhelmed. Mahiro looks towards the classmate and finds out that it is none other than Momiji. Mahiro is overjoyed and calls Momiji her savior. One of the girls, Nadoka, asks Momiji if Mahiro is a friend of hers, and Momiji confirms it saying that she'll introduce her later. Another girl, Minori, apologizes to Mahiro for what just happened.

Mahiro thanks Momiji for saving her, while Momiji calls this entire thing a surprise. Miyo and Asahi show up at Mahiro's desk as well, continuing by saying that they never thought that Mahiro would become their classmate. Mahiro is happy to see them, and claims that it was a surprise for her as well. Momiji points out that she had no idea that Mahiro had dropped out of school due to an illness and studied for awhile at home. Mahiro is confused, then realizes that that must be the cover story that Mihari mentioned. Mahiro plays along with it by claiming that she might not be in perfect health yet. She also claims that she was just getting well enough to do things again when she met Momiji and says that that's the reason why she was so late enrolling.

Momiji says that it is no wonder that Mahiro stayed inside all day, a statement which Mahiro laughs at. Miyo says that it must've been tough, and wonders if Mahiro is really okay now, commenting that she looks a little pale. Mahiro says that she is fine, claiming that she is just sleepy. Momiji comments that school does start pretty early. Asahi adds that Mahiro is a lazy bum after all, leading to her getting whacked on the head by Momiji.

Asahi decides that she'll share some of her energy with Mahiro, which leaves Mahiro confused. Asahi gives Mahiro a "huggy-wuggy" in which she hugs Mahiro and pulls Mahiro's head into her chest while doing so. Mahiro becomes happy by it and thinks to herself that Asahi smells like a summer day. Momiji abruptly pulls Mahiro away from Asahi and tells Asahi not to do that. Asahi isn't listening to that, and tells Momiji that it's her turn, doing the same to her. Miyo becomes extremely aroused by both hugs and collapses on Mahiro's table in ecstasy. Mahiro notes to the others that they may have killed Miyo.

At the end of the day, Mahiro reflects on her first day. She notes that class was less stressful than she thought, though she notes that they were going easy on her since she's a transfer student. She also notes how she was worried about breaks, but thanks to Momiji and her friends, those weren't bad either. After the final class, Mahiro slumps forward on her desk and sighs in relief that she is finally done and that she made it. Momiji suggest that the four of them walk home together, and Mahiro agrees. As they walk down the stairs, Mahiro smiles and notes that she is glad that these three were here. She knows that she would've been totally helpless without them. She starts to think that if it stays like this, maybe school won't be so bad.

Mahiro then feels a twinge and lets the others know that she needs to use the restroom. Struggling to hold it, she instinctively runs into the boys room by mistake before correcting herself. She remembers that she now has to use the ladies room, but notes that it still makes her feel like a criminal. Before she can go in however, Momiji, Asahi, and Miyo pass in front of her deciding to go as well. Mahiro is surprised, then remembers that girls always go to the bathroom together. Mahiro decides that going alone is one thing, but that she's way too self-conscious to go in a group.

Momiji asks Mahiro what's up, and Mahiro claims to be fine after all. Momiji accepts her answer and tells Mahiro she won't be long, and Mahiro waves her off despite secretly struggling to hold it in. On the walk home, the others talk about the recent trip to the café. Momiji asks Mahiro if she's listening, which Mahiro isn't due to continuing to hold it in. She tries to persuade herself that she's doing the right thing.

Eventually, Momiji points out that they made it to Mahiro's house, and Mahiro is relieved that she was able to hold it all the way. Mahiro tells the others that she will see them tomorrow, and the girls say the same. Mahiro reaches her door, but before she opens it she realizes that she said "tomorrow" without even realizing it. She then remembers that there is no time for that and remarks that she's got to go, pushing the door open in a hurry.

Mihari is waiting inside and begins to welcome Mahiro home, when Mahiro crashes into her much to the surprise of both of them. Mihari tells Mahiro that that hurt, and asks her why she is running like that. At that moment, Mahiro can't hold it any longer and wets herself in front of Mihari while sitting on the floor. Mihari finally understands why Mahiro was in such a rush.

Later, Mahiro lays under her covers crying over what happened. Mihari tries to comfort her by saying that she's not mad, but Mahiro just remains silent. Mahiro thinks to herself how it was a slightly bittersweet first day of school.

Later still, Mihari cleans up the floor where Mahiro had her accident.

Characters

 * Mahiro Oyama
 * Mihari Oyama
 * Momiji Hozuki
 * Asahi Ōka
 * Miyo Murosaki
 * Mari Nishinomiya
 * Aoi Tachikawa
 * Nodoka Fushimi
 * Satsuki Tadaka
 * Minori Shiina
 * Nemu Fujimi
 * Yuta Sakurada

Trivia

 * First appearances of Mari Nishinomiya, Aoi Tachikawa, Nodoka Fushimi, Satsuki Tadaka, Minori Shiina, Nemu Fujimi, and Yuta Sakurada.
 * Momiji talks about when the girls met for parfaits in "Mahiro and the Middle Schoolers".