ONIMAI: I'm Now Your Sister! poster

TV series

ONIMAI: I'm Now Your Sister!

2023TV-141 season7.4 / 10

When lazy, erotic-game loving Mahiro Oyama is transformed into a girl by his younger scientist sister's experiments, he becomes determined to change back, only to recognize that with his new opportunity, he may want to turn his life around.

Streaming, rental and purchase options

Where to watch in United States

Checked Jul 22, 2026

ONIMAI: I'm Now Your Sister! is available to stream on Crunchyroll Premium (Via Amazon Prime) in United States. You can also buy it from Amazon. Use the direct links below to open the provider.

Availability and prices can change. Confirm the details on the streaming service before you subscribe, rent or buy.

Synopsis

When lazy, erotic-game loving Mahiro Oyama is transformed into a girl by his younger scientist sister's experiments, he becomes determined to change back, only to recognize that with his new opportunity, he may want to turn his life around.

Season 1 episodes

Choose an episode, then use the watch options above for the show.

Episode 1

Mahiro's Confusing New Body

23m7.3 / 10

We follow Mahiro Oyama, an unemployed good-for-nothing shut-in, who not only hasn't left the house in two years, but is also exceedingly addicted to gross video games. One afternoon, he wakes up and notices that his body feels a little off. Finding that strange, he goes to reach for his tablet, but what does he see in his reflection, but an adorable young lady. I wonder what lies in store for the "former" big brother, Mahiro as he's thrust headfirst into his new life as a girl.

Episode credits

Directed by Shingo FujiiWritten by Michiko YokoteGuest stars Yoshie Saito, Hiroaki Miura, Hisayoshi Suganuma, Emiri Suyama

Where to watch ONIMAI: I'm Now Your Sister!

Episode 2

Mahiro's Time of the Month

23m5.0 / 10

As Mahiro stumbles through his new life as a girl, he finds himself gradually beginning to get into the swing of things. Realizing this, however, prompts him to try and reclaim some of his masculinity. He tries, in futility, to engage his core and do a sit-up, but ends up with a stomachache instead. Seeing his condition worsen rapidly before her eyes, Mihari has an epiphany. She realizes that his pain may actually have something to do with fact that almost a month has passed since Mahiro turned into a girl...

Episode credits

Directed by Eri IreiWritten by Michiko YokoteGuest stars Kumiko Nakane, Yoshie Saito, Reimi

Where to watch ONIMAI: I'm Now Your Sister!

Episode 3

Mahiro's Close Encounter

23m3.8 / 10

Mahiro makes a mad dash for the bathroom, but when he opens the door, he finds the facilities are already occupied by a high school girl he's never met. This bold fashionista turns out to be Kaede, Mihari's old classmate from middle school. Mahiro is initially a little nervous around her, but as he gets to know her, he learns how much of a nice person she is and becomes quite attached to her. Then, out of nowhere, Kaede asks "You've never done it before, have you?" and begins to scooch closer to a puzzled Mahiro. I wonder what she's about to do next...

Episode credits

Directed by Yasuhiko AkiyamaWritten by Miharu HiramiGuest stars Emiri Suyama, Erisa Kuon, Yuuya Uchida, Hironari Nemoto

Where to watch ONIMAI: I'm Now Your Sister!

Episode 4

Mahiro's New Friend

23m6.0 / 10

Mahiro loses to Mihari in a video game, so he has to do the grocery shopping this week as punishment. As an unemployed, good-for-nothing shut-in, the task at hand is daunting, but he plucks up the courage and makes his way towards the supermarket. The size of the crowd, however, makes his resolve waver and Mahiro finds himself cowering outside the store entrance. It is then that a young boy (?) around his age, wearing a baseball cap, comes to the rescue and offers him a helping hand. Thanks to the boy's (?) help, Mahiro is able to buy the groceries he needs and is just about to head home, when Kaede suddenly shows up. Seemingly, out of nowhere.

Episode credits

Directed by Hayato KakitaWritten by Michiko YokoteGuest stars Erisa Kuon, Emiri Suyama, Kousuke Goto, Enako

Where to watch ONIMAI: I'm Now Your Sister!

Episode 5

Mahiro Discovers Adventure and Social Gatherings

23m6.5 / 10

In a rare turn of events, Mihari wakes up one morning to find Mahiro has gotten up before her. Since the corner store was going to start selling clear files from his favorite anime that day, he had woken up early to go pick them up before they sold out. Mihari is overwhelmed with joy to see Mahiro going outside of his own accord. On his way back from buying the clear files, Mahiro stops by an arcade for the first time since middle school. He's enjoying a rhythm game when suddenly he senses a man standing watching him from behind. A few minutes go by when he feels a tap on the shoulder...

Episode credits

Directed by Komawo YukihiroWritten by Michiko YokoteGuest stars Erisa Kuon, Mitsuki Nakamura, Yuri Ise, Ren Arata

Where to watch ONIMAI: I'm Now Your Sister!

Episode 6

Mahiro Goes Back to Middle School

23m6.5 / 10

Momiji shows up at Mahiro's house with her two classmates, Asahi Ohka and Miyo Murosaki, to invite him out for parfaits.

Episode credits

Directed by Nobuyoshi AraiWritten by Miharu HiramiGuest stars Rina Tsukishiro, Misaki Watada, Miyuu Takatsuki, Sayako Tojo, Rena Aoshima, Rika Abe, Rin Mizuki, Yuuki Yamamoto

Where to watch ONIMAI: I'm Now Your Sister!

Episode 7

Mahiro's Role-Playing Game

23m6.5 / 10

Just when Mahiro is beginning to get used to middle school life again, finals are upon them. Despite his initial blasé attitude, Mahiro finds himself reluctantly handing in a 80% blank answer sheet after having slept through the entire first exam.

Episode credits

Directed by Ayumu UwanoWritten by Miharu HiramiGuest stars Misaki Watada, Miyuu Takatsuki, Rena Aoshima, Rika Abe, Rin Mizuki, Mia Sakurai, Rika Nagae

Where to watch ONIMAI: I'm Now Your Sister!

Episode 8

Mahiro's First Girls Sleepover

23m6.5 / 10

It's finally winter break and Mahiro is excited to get into his Winter Vacation Mode. Unbeknownst to him, however, Mihari invites Momiji and the others over for a sleepover. She hopes this will prevent a potential relapse into his old, shut-in ways.

Episode credits

Directed by Hironori TanakaWritten by Michiko Yokote

Where to watch ONIMAI: I'm Now Your Sister!

Episode 9

Mahiro Rings in the New Year

23m3.8 / 10

It's Christmas and Mahiro is shocked to hear his own little sister has a date. Unable to shake his unease, he follows her through the festive hustle and bustle in secret, with Momiji as his escort in tow. Who could Mihari possibly be meeting with?

Episode credits

Directed by Yasuhiko AkiyamaWritten by Michiko YokoteGuest stars Yoshie Saito, Mitsuki Nakamura

Where to watch ONIMAI: I'm Now Your Sister!

Episode 10

Mahiro Ponders Boobs and Identity

23m6.5 / 10

It's the start of the third semester and winter uniforms are now in effect. For Mahiro and the girls at school, this means braving the cold winter air in mandatory skirts. Who knows how Miyo will react when he and Momiji show up in matching scarves, too.

Episode credits

Directed by Aose SakaguchiWritten by Miharu HiramiGuest stars Rina Tsukishiro, Misaki Watada, Miyuu Takatsuki, Sayako Tojo, Rena Aoshima, Rika Abe, Mia Sakurai, Karin Oda

Where to watch ONIMAI: I'm Now Your Sister!

Episode 11

Mahiro Pretties Up

23m6.0 / 10

Horoscopes are all the rage at school right now, and Mahiro is curious to see what all the fuss about. According to his forecast, an important occasion is on the horizon and he may be in for a surprise or two. But what occasion could it be alluding to?

Episode credits

Directed by Komawo YukihiroWritten by Miharu HiramiGuest stars Rina Tsukishiro, Misaki Watada, Miyuu Takatsuki, Sayako Tojo, Rena Aoshima, Rika Abe, Rin Mizuki, Mia Sakurai

Where to watch ONIMAI: I'm Now Your Sister!

Episode 12

Mahiro's Future as a Sister

23m6.5 / 10

Mahiro and the girls take a trip to a Japanese inn over spring break. First they hit the town in their yukata, before heading to the open-air bath to detox. However, things go south when Mahiro begins to feel a familar tingling sensation between his legs.

Episode credits

Directed by Shingo FujiiWritten by Michiko YokoteGuest stars Sachiko Okada, Kumiko Nakane, Kosuke Kobayashi

Where to watch ONIMAI: I'm Now Your Sister!

Episode information updated Jul 23, 2026

More about ONIMAI: I'm Now Your Sister!

Cast

Marika KounoMahiro Oyama (voice)
Kaori IshiharaMihari Oyama (voice)
Hisako KanemotoKaede Hozuki (voice)
Minami TsudaMomiji Hozuki (voice)
Kana YuukiAsahi Ohka (voice)
Natsumi HiokaMiyo Murosaki (voice)
Hiroaki MiuraSeme (voice)
Hisayoshi SuganumaUke (voice)

Credits

Written by
Michiko Yokote, Miharu Hirami

Production details

Status
Ended
Series type
Scripted
Episodes
12
Original language
Japanese
Original title
お兄ちゃんはおしまい!

Networks & production

  • AT-XJapan
  • Studio BindJapan
  • EGG FIRMJapan
  • IchijinshaJapan
  • TOHOJapan
  • Hakuhodo DY Music & PicturesJapan

Themes

age changeanimebased on mangaecchienragedgender swapgrandjapanese junior high schooler