He was a hikikomori neet and loner, until he woke up one morning as a little girl thanks to his [younger sister](https://anilist.co/character/130823/Oyama-Mihari) drugging him.

Mahiro Oyama was just a normal erotic-game loving dude…until he woke up one morning as a woman! Turns out his mad-scientist little sister, Mihari, tried out one of her new experiments on him…with a disastrous outcome, as far as Mahiro’s concerned! But Mihari is as determined to study him as he is determined to go back to his shut-in, game-playing life, and one thing’s for sure…life is going to get a whole lot weirder from here on out! 
 
(Source: Kodansha USA)

__Height:__ 158 cm
__Agency:__ Aoni Production

[Profile (Aoni)](https://www.aoni.co.jp/search/kohno-marika.html) | [Twitter](https://twitter.com/marika_0222) | [Instagram](https://www.instagram.com/marika_kohno_0222/) | [Wiki (en)](https://en.wikipedia.org/wiki/Marika_Kouno) | [Wiki (jp)](https://ja.wikipedia.org/wiki/高野麻里佳)

She is part of the seiyuu idol group [**Earphones**](https://anilist.co/staff/195973/) (イヤホンズ) with fellow voice actresses [Rie Takahashi](https://anilist.co/staff/119331) and [Yuki Nagaku](https://anilist.co/staff/119370), originally formed for the anime [Sore ga Seiyuu!](https://anilist.co/anime/21009).

**Non-anime roles:**
• Primavera - Memento Mori (VG)

[Profile](https://www.aoni.co.jp/search/reimi.html)

Mahiro Oyama was just a normal erotic-game loving dude…until he woke up one morning as a woman! Turns out his mad-scientist little sister, Mihari, tried out one of her new experiments on him…with a disastrous outcome, as far as Mahiro’s concerned! But Mihari is as determined to study him as he is determined to go back to his shut-in, game-playing life, and one thing’s for sure…life is going to get a whole lot weirder from here on out!
 
(Source: Kodansha USA)
 
Note: Includes 57 extra chapters.

An anthology comic of Onii-chan wa Oshimai! by various mangaka.
 
Volume 1 (2021-05-27) 
Cover Illustration: Namori 
Color Illustration: Yui Hara, Shiromanta, Bell Izumi 
1. 3-bai★Push! (3倍★プッシュ!) [Namori] 
2. Onii-chan wa Umitai!? (お兄ちゃんはうみたい!?) [Koume Fujichika] 
3. Mahiro to Minority (まひろとマイノリティ) [Natsu Tadano] 
4. Mahiro to Keika Kansatsu (まひろと経過観察) [Taku Kawamura] 
5. Himitsu no Hand Sign (秘密のハンドサイン) [Masakuni Igarashi] 
6. A letter for you [Waka Kakitsubata] 
7. Oyama Mahiro wo Kisekaetai! (緒山まひろを着せ替えたい!) [Norito Asazuki] 
8. Wasurerarenai Kanshoku (忘れられない感触) [Nekoume] 
9. Mahiro to Mahiri (まひろとまひり) [Tsuchii] 
10. Mahiro to Imaginary (まひろとイマジナリー) [Misaki Mori] 
11. Mahiro to Kyoufu no Misshitsu (まひろと恐怖の密室) [Kometsubu] 
12. Mihari to Aibou (みはりと相棒) [Shinichi Yuuki] 
13. Mahiro Love Letter (まひろラブレター) [Kina Kobayashi] 
14. Mahiro to Dankatsu (まひろと男活) [Suzu Yuuki] 
15. Mahiro to Kourei no Are (まひろと恒例のアレ) [Suka] 
 
Volume 2 (2022-04-27) 
Cover Illustration: bb Kuroda 
Color Illustration: Cool-kyou Shinja 
 
Volume 3 (2023-01-07) 
Cover Illustration: Yui Hara 
Color Illustration: bb Kuroda 
 
Volume 4 (2023-11-27) 
Cover Illustration: Hiroshi Hiroyama 
Color Illustration: Hori 
 
Volume 5 (2024-09-27) 
Cover Illustration: Ryou Imamura 
Color Illustration: Cherry Arai 
 
Volume 6 (2025-07-26) 
Cover Illustration: Muchimaro 
Color Illustration: Kouhei Shibata, Tsuchii, Ayase Totsuki 
 
Volume 7 (2026-05-27) 
Cover Illustration: Cool-kyou Shinja 
Color Illustration: Zurikishi

Specials chapters of Onii-chan wa Oshimai! bundled with the mini dramas CD sold during Comic Market.

Special manga drawn for the Blu-Ray release of the anime Onii-chan wa Oshimai!.

Includes: 
1) まひろちゃんお誕生日会場 (2022 March 6) 
2) みはりちゃんお誕生日会場 (2022 April 22) 
3) あさひお誕生日会場 (2022 May 5) 
4) みよちゃんお誕生日会場 (2022 June 18) 
5) かえでちゃんお誕生日会場 (2022 September 12) 
6) もみじお誕生日会場 (2022 October 20) 
7) なゆたんお誕生日会場 (2022 November 23) 
8) まひろちゃんお誕生日会場 2023 (2023 March 6) 
9) みはりちゃんお誕生日会場2023 (2023 April 22)

A booklet bundled with the Onii-chan wa Oshimai! volume 7 special edition.