Mahiro and the Seasonal Attire

Mahiro and the Seasonal Attire (まひろと衣替えの季節, Mahiro To Koromogae No Kisetsu) is Chapter 45 of Onimai: I'm Now Your Sister!. It was originally published on Pixiv on October 24, 2020.

Summary
With Spring in full bloom, Mahiro and her friends begin to switch to their summer uniforms.

Plot
The morning before returning to school after Golden Week, Mahiro eats her breakfast in peace. She notes that the morning after a holiday is always so melancholy. Mahiro thanks Mihari for the breakfast, and Mihari says "of course". Mihari tells Mahiro that she's laid out her clothes for the day, and Mahiro heads upstairs thanking her. Mahiro begins to put on her uniform jacket, then notices something that catches her attention.

Mihari has replaced the long sleeved jacket of the uniform with a vest. Mihari says that it is very nice and asks if it's cool and refreshing, but Mahiro is confused about the uniform being different today. Mihari explains that this is the spring version of the uniform, commenting that it's a bit too warm for the winter uniform. Mahiro is amazed that it is already time to change uniforms. Mihari points out that she is is in short sleeves too, having switched out her usual lab coat for one with short sleeves, and calls it cool. Mahiro tells her that she should really stop wearing the lab coat entirely.

At school, Asahi says good morning to everyone. Mahiro notes that Asahi is in her summer school uniform already, with no vest and short sleeves instead of long ones. Asahi says that it is much cooler. Momiji says that this is the time where everyone does their own thing. She is wearing the spring uniform with no vest, while Momiji is wearing a sweater over her spring uniform. Mahiro notes that the sweater is a good look too.

Mahiro notices Nayuta wearing the same outfit she is, and is overjoyed that they match. Momiji sees this and quickly takes out her vest from her bag and appears in front of Mahiro so they can match as well, asking Mahiro if it's still a little chilly. Mahiro is confused while Miyo laughs at the situation.

In the locker room before gym class, Mahiro notes that gym clothes are still all over, and Miyo confirms that will be the case until the end of the month. Miyo also says that's she still a little worried about summer uniforms though, and Mahiro asks her why that is. Mahiro sees Miyo's large bust as she puts on her track suit, and understands. Miyo explains that she's also gained weight recently and that it's harder to not to stand out in light clothing. Mahiro closes her eyes, trying to be considerate, thinking to herself that she knew that that was the reason.

Miyo adds that swim classes will start before too long, which gets Mahiro worried. She knows that that means swimsuits, and fears having to wear one as well. She imagines a newpaper article titled "Real Life Nightmare! Cross-Dressing Pervert Exposed in School Swim Class".

Miyo then asks Mahiro if, by any chance, she went up in size recently. Mahiro is confused, and Miyo explains that she happened to see the adult bra Mahiro was wearing at the barbecue after her accident. Mahiro explains that Mihari got it for her, and that it does fit a lot better. She squishes her bust and starts think that maybe she did get bigger.

Miyo begins feeling Mahiro's bust from behind, causing Mahiro to laugh. Miyo then suggest to Mahiro that they go somewhere after school, much to Mahiro's surprise.

After school ends, Mahiro sits at her desk and wonders what Miyo means where she suggested that they go somewhere after school. She wonders if Miyo is the voyeur type. Miyo suddenly appears at Mahiro's desk and asks her if she's ready to go, causing Mahiro to shriek.

The shriek catches Momiji's attention, and she wonders what's going on as she sees Miyo push Mahiro out of the classroom. Asahi tries to call out to them, but Momiji puts her hand over her mouth and orders her to be quiet. Momiji notes that this is very suspicious and notes that they should tail them. Nayuta tells Momiji that she has the best ideas sometimes.

As Asahi, Momiji, and Nayuta tail Mahiro and Miyo, they see them going into a mall, leading Momiji to wonder if they're going shopping. Momiji sees them going into the clothing section and realizes what is going on.

Mahiro and Miyo have entered into a fancy lingerie store and are amazed by everything inside it. Miyo notes that she's always wanted to come here, and remarks that it's got such a mature atmosphere. Miyo says that she could never work up the courage to set foot inside this place alone. She explains that she doesn't like being looked at, but she does like cute lingerie. Mahiro notes that she is starting to feel bad about this.

Miyo suggests to Mahiro that since they're here they should get her properly fitted, much to Mahiro's shock. Miyo calls over a saleslady and asks if she can measure Mahiro first, despite Mahiro's protests. Miyo adds that they let you try on things as well and asks Mahiro what she thinks of one. Mahiro says that she can't do this, but Miyo says that she'll be right here with her. Mahiro attempts to protest, but to no avail.

As the two are heard giggling about how good they look, Momiji, Asahi, and Nayuta fall into a deep gloomy state as they are not developed enough to enjoy it as well. Momiji suggests that they go home, and the "Flat Chest Squad" leaves.

Meanwhile, Mahiro is in heaven thanks to the whole experience. Miyo notes that they gave them a catalogue, so now they can save up their allowance and come back for something nice. Mahiro ultimately has mixed feeling about the idea of coming back, regardless of how she feels.

At home, Mahiro slumps forward on the couch and notes that she went though all that with nothing to show for it, except the lingerie catalogue. As she starts reading though it, Mihari walks in and is shocked at the sight of Mahiro reading something like that. Mihari asks Mahiro what she's thinking of and says that she'll buy Mahiro whichever she likes, much to Mahiro's shock.

At the Hozuki household, Kaede calls out to Momiji asking if she's seen her bra anywhere. Momiji is revealed to have taken it, holding it up in jealously that her sister is so developed while she's still flat as a board.

Characters

 * Mahiro Oyama
 * Mihari Oyama
 * Kaede Hozuki
 * Momiji Hozuki
 * Asahi Ōka
 * Miyo Murosaki
 * Nayuta Tenkawa
 * Nodoka Fushimi
 * Nemu Fujimi
 * Mai Yasaka
 * Aoi Tachikawa

Trivia

 * Mahiro indicates that this is the first day back after the end of Golden Week, indicating that the events of this chapter take place shortly after the events of the previous chapter "Mahiro and the Barbecue Secret".
 * This is the first episode where Mahiro and her friends wear their spring school uniforms (though Asahi wears her summer uniform instead), as well as the first time that Mihari wears her short-sleeved lab coat.
 * Mahiro is still trying to be more considerate by not looking at her friends while they change in the locker room, first having done so in "Mahiro and the School Physical".
 * Miyo notes that swim classes will start soon, this would happen in "Mahiro and Swim Class (Part 1)". Ironically the thing that Mahiro feared most would almost occur during that class, exactly as she imagined it in this chapter.