Keiko Aizaki, also credited as Keiko Aisaki, is a Japanese writer known for creating the controversial manga and anime series The Rapeman. Aizaki is credited as the story writer for The Rapeman, which was illustrated by artist Shintaro Miyawaki. The manga was serialized in the magazine Leed Comic from 1985 to 1992. Over its seven-year run, the series was compiled into thirteen tankobon volumes.

The Rapeman is Aizaki's most recognized and only widely documented work. The narrative follows Keisuke Iwasaki, a high school teacher by day who operates a clandestine vigilante service called "Rapeman Services" with his uncle at night. The service accepts client commissions to punish wrongdoers through sexual assault, operating under the motto "righting wrongs through penetration". The manga employs an episodic format, with each chapter depicting a different commission and resolution.

The series spawned multiple adaptations, confirming Aizaki's role in a media franchise. An original video animation adaptation was produced in 1994, consisting of two episodes. A series of nine live-action direct-to-video films were also released between 1993 and 1996. In 2000, a sequel titled The Rapeman 2 began serialization in Penthouse magazine, though this sequel was not collected into book format.

Significant ambiguity surrounds Keiko Aizaki's identity and creative background. Aizaki has not been credited for any writing activities before or after The Rapeman, leading to speculation about whether Aizaki is a real person or a pseudonym. Some fans have suggested that the female-sounding name may have been used to soften the controversial content's image, though there are accounts of a woman appearing in relation to the live-action film productions. With the illustrator Miyawaki having passed away in 2010, the true nature of Aizaki's identity remains unconfirmed. No verified information exists regarding Aizaki's biography, other creative works, or personal background beyond the credit as the scenario writer for The Rapeman.