Mahiro's Confusing New Body (manga)

Mahiro's Confusing New Body (まひろとイケない身体, Mahiro To Ikenai Karada) is Chapter 1 of Onimai: I'm Now Your Sister. It was originally published on Pixiv on February 25, 2017.

Summary
Mahiro Oyama, a male otaku and a slacker, wakes up one morning to discover that one of his younger sister's experiments has transformed him into a middle-school aged girl.

Plot
Mahiro Oyama, drags himself out of bed to look at his clock. It reads 12:26 PM and Mahiro notes that it is afternoon already. Mahiro groans and notes to the reader that one day he woke up and had been turned into a girl.

Mahiro tests out his voice only to find it different. He notes that he's really out it and deduces that he must've gotten sick or something. He reaches for a bottle of water, and then catches his reflection in the TV by his bed. Instead of showing his normal appearance, it shows that of a cute young girl.

Mahiro is shocked and looks around to make sure that there is no one else in the room. Mahiro can't believe that this cute girl is him, saying that he is "a red-blooded eroge-loving, fiercely independent guy". He believes it to be movie makeup, but notices that he's shorter as well. He then squishes his chest and notes that the supposed bust he now has also feels real, but notes that he is not very experienced in this area.

To make sure, he decides to take a look at his crotch to confirm it and removes his pants to do so. Right before he can look, his younger sister Mihari Oyama comes in to say good morning to him. She catches him with his pants around his ankles, and he begs her not to get the wrong idea. Mihari looks him over, and then flips up the front of his now oversized shirt to check his crotch as well. She notes that Step #1 is a success, conforming that Mahiro has been transformed fully into a girl.

Mihari notes to Mahiro that he, or rather she, turned out very cute (looking like a middle-schooler). Mahiro is shocked and realizes that Mihari drugged her to turn her into this. Mihari confirms this and explains that she slipped the drug into Mahiro's dinner.

Mahiro explains to the reader that her younger sister Mihari is a genius who skipped a bunch of grades and went to college early, and that it seems that she is doing some questionable research.

Mahiro asks Mihari what she thinks she is anyway. Mihari is bluntly honest and tells Mahiro that she is an unemployed, good-for-nothing shut in who hasn't left the house in two years, who sits around playing eroge all day an doesn't even have a job.

She asks Mahiro why she wouldn't just get a job, and Mahiro asks how she possibly could with this new body. Mahiro thinks that Mihari means to use the new body, imagining doing an erotic webcam show, but Mihari shuts that idea down immediately. Mihari tells Mahiro to just cooperate with the experiment and to think of it as a clinical trial. She says that she can't promise quick results, but that she'll still make a good citizen of Mahiro yet. She also tells Mahiro not to worry about her new body, as without the drug she (likely) will eventually change back.

She suggests that in the meantime, Mahiro should try to have some fun with it and suggests living her life as a girl for a bit. Mahiro considers it, while Mihari suggests that for starters she could try getting up a little earlier. Mahiro laughs off the suggestion and decides to have fun instead with some of her eroge games. She tells Mihari not to come in without knocking from now and tells her to scram. Mihari groans a bit, but decides to have fun as well by telling Mahiro one last thing. She explains that the the female orgasm is up to one-hundred times more powerful than the male one, and that if she rushes into things without being properly prepared, she might not be able to handle the shock. Mihari notes with love that they wouldn't want Mahiro to end up broken and slams the door shut.

Mahiro is shocked but starts focusing on her eroge game. Despite her best efforts, she cannot get aroused by it and remarks that it is torture. Mihari in the meantime watches from a webcam she installed in Mahiro's room wondering what will happen next, compiling data as part of her "Onii-chan Rehabilitation Project". While she does, Mahiro notices the camera, wondering how long it has been there.

Characters

 * Mahiro Oyama
 * Mihari Oyama

Trivia

 * First appearance of Mahiro Oyama and Mihari Oyama.