Mahiro and Swim Class (Part 2)

Mahiro and Swim Class (Part 2) (まひろと水泳教室（後編）, Mahiro To Suiei Kyōshitsu (Kōhen)) is Chapter 50 of Onimai: I'm Now Your Sister!. It was originally published on Pixiv on March 27, 2021.

Summary
Mahiro's "comrade" suddenly regrows while in the pool with the other girls.

Plot
While in the pool for swim class, Mahiro is in absolute shock that her "comrade" has sprung up again, now of all times, and notes that this is bad, real bad. She notes that Nayuta is of no help here, and wonders if she can get convince the teacher to help her. Rin asks Mahiro what's wrong, and if she got a leg cramp. Being so close to Rin causes Mahiro's "comrade" to start getting hard, causing Mahiro to panic even more.

Mahiro turns around, much to Rin's confusion, noting that she can't talk to her like this as it's been so long that her "comrade" is going crazy. Mahiro mentally tells herself to calm down, and decides to just find a way to get out of the pool for now. She figures that she could always power through and pretend like she has to run to the restroom, covering it with her hands. After seeing Nemu get out of the pool, she realizes that that won't work, as she'd be completely defenseless on the ladder.

Mahiro tells herself to get a grip, and let her mind race at the unexpected crisis. Noting that she can't let anyone see and needs consideration, she tells herself to use her intelligence and experience, and comes up with an inspiration.

Mahiro claims to Rin that she's unexpectedly started her period. Rin understands and tells Mahiro to get out of the water where she can rest. Mahiro says that the thing is that she doesn't want anyone to see because it might dribble out. Miyo puts her hand over her mouth in shock at hearing this, while Rin tells Mahiro to stay right there and runs to fetch a towel. Nayuta wonders what Mahiro means by "dribble out", but Miyo tells her to be quiet.

Rin returns with a towel, and Mahiro asks if Nayuta can help her since she's on the health committee. Mahiro notes that this is the perfect defense. The other girls will turn away out of consideration while Nayuta blocks the view from behind just in case. Plus, with a towel just a moment away she's free. Mahiro notes that it was a little slapdash, but knows that she had to improvise.

As Mahiro climbs out of the pool, Nayuta looks directly at Mahiro's crotch and sees the outline of Mahiro's "comrade", putting her in a daze as she gets confused.

Rin helps Mahiro with the towel and asks if she'll be okay, to which Mahiro says that she will be. She asks if she can go ahead and change clothes, and Rin says that that sounds best. She tells Mahiro to have the health officer, Nayuta, escort her just in case. Nayuta is still in a daze, but snaps out of it when Rin calls out to her and understands what she needs to do. As Nayuta escorts Mahiro inside, Asahi asks Momiji if they are going to the restroom. Momiji tells her to be quiet and not ask questions.

Once they are inside the locker room, Mahiro sits on the ground and breathes a sigh of relief that she is safe. Nayuta understands that the drug must be wearing off. Mahiro says that it seems so and asks Nayuta to look the other way for a second while she changes back into her uniform. Nayuta understands the bulge she saw earlier must've been Mahiro's "comrade", and Mahiro wonders what she should do now. She notes that even if she changes back into her uniform, there's still a risk. If there's even one mistake, its over. Nayuta asks Mahiro if she could just hide it under her skirt. Mahiro says that she normally could, but whispers that it can get hard on its own. Nayuta understands, and decides that in this case it is time for her to step up. She remarks that it wouldn't do for the others to see the next step and leads Mahiro to the restroom, much to Mahiro's confusion.

Nayuta locks them in a private stall in the restroom, making Mahiro confused. She wonders if it is leading to something inappropriate, imagining a lewd scenario where Nayuta says that once they've tired it out it'll go away. Nayuta tells Mahiro to remove her underwear, leading Mahiro to tell her that this is a criminal offense. Nayuta instead takes out a roll of duck tape, much to Mahiro's surprise, and says that they'll tuck it back and secure it with this. Mahiro shrieks with dread and puts her hands over her private area in shock. She screams the whole time that Nayuta tapes her "comrade" in place.

Mahiro returns to class, noting that in the end she stayed how Nayuta fixed it all day. She also notes that she couldn't keep her mind off it though. She wonders if she should go home now if she can, as she doesn't know what is going to happen to the rest of her body. Miyo asks Mahiro if she's alright now, causing Mahiro to panic. As Mahiro looks at Miyo and the other girls, she starts to have erotic feelings for them and finds herself composing a haiku about them in her mind: "The scent of chlorine, and their damp, still messy hair, a post-pool delight". Mahiro giggles and notes that this is a little erotic, but then becomes horrified and notes that this is bad. She wonders what blasphemy this is, and thinks that she needs to drag her mind out of the gutter. Miyo and Nayuta look at Mahiro in confusion.

Mahiro decides that she just needs to lay her eyes on wholesome little Asahi and looks at her. She sees Asahi sighing, and wonders what is wrong with her. Momiji explains that Asahi apparently forgot a change of underwear, as usual. Asahi notes that it's so breezy.

Mahiro giggles at the thought of Asahi not wearing panties, but then suddenly becomes shocked. She realizes in horror that the drug wearing off is also causing her erotic feelings about girls that she had as a guy to return, and calls herself scum. Momiji sees her reaction and gets confused.

Mahiro races home, afraid of what might happen next. She bursts through the front door huffing and puffing, while Mihari asks her what happened with school. Mahiro demands the medicine and says that she needs it quickly. Mihari gets it for her, but wonders what happened. Mahiro sighs in relief after she takes the medicine, noting that now she can finally relax. She notes that male instincts are fearsome indeed.

Mihari notes that as long as Mahiro is okay with it, leading Mahiro to realize the full implications of what she just did. Mahiro has extended her time as a girl and cringes, telling Mihari to just forget that she heard anything. Mihari just laughs and encourages Mahiro to keep it up for one more cycle.

Soon after, Mahiro winches in pain as she peels off the duck tape holding her "comrade" in place.

Characters

 * Mahiro Oyama
 * Mihari Oyama
 * Momiji Hozuki
 * Asahi Ōka
 * Miyo Murosaki
 * Nayuta Tenkawa
 * Rin Minakata
 * Nemu Fujimi
 * Mai Yasaka
 * Miyako Nagase
 * Aoi Tachikawa

Trivia

 * The events of this chapter takes place directly after the events of the previous chapter "Mahiro and Swim Class (Part 1)".
 * This chapter marks the second time that Mahiro has been able to fake having her period as an escape scenario with Rin, the first time being in "Mahiro's Difficult Class". The first time wasn't intentional though.
 * When the girls turn away, it becomes clear the final girl in the beginner swim group was Aoi. In the previous chapter "Mahiro and Swim Class (Part 1)", her hair wasn't colored in the right color which made it impossible to tell that it was her.
 * This chapter marks the second time that Mahiro composes a haiku in her mind about her life, the first time was in "Mahiro's Relaxing Day Off".
 * This chapter marks the second time that Mahiro has consumed another dose of the feminization drug to remain female, the first time being in "Mahiro's Panic! At the Hot Spring (Part 2)". It also marks the third time overall that Mahiro has consumed the drug.