The mysterious Kougami Foundation approaches Eiji and begins assisting him in his fight against the Greed, though their true motives are not clear. When metallic creatures known as the Greeed awaken after their 800-year slumber to attack humans and feed off of their desires, the disembodied arm of the Greed named Ankh gives Eiji a belt and three Medals to fight the other Greed as Kamen Rider OOO. PlotĮiji Hino is a traveling man who has no place to call home and a tragic past. For the 999th and 1000th episodes, various guest stars with the kanji for thousand ( 千, chi ?) in their name were featured: Chiaki, Chisato Morishita, Chinatsu Wakatsuki, and the owarai duo, Harisenbon ( sen also being Japanese for 1000). However, due to the 2011 Tohoku earthquake and tsunami, the airing of this episode was postponed by one week to April 3, 2011.

The episode was originally set to premiere on March 27, 2011. The 28th episode of Kamen Rider OOO serves as the 1000th episode of the Kamen Rider Series since Kamen Rider premiered on April 3, 1971. The title OOO signifies the three medals that the main Kamen Rider uses to transform as well as being representative of the infinity symbol with an additional circle.

Both 'OOO' and 'Ooz' are intended to be read as 'O's', referring to the multiple uses of the letter O in the title as well as 'multiple kings' ( 王ｓ, Ōzu ?). Unlike several previous Heisei Rider Series, no alternate name has been given yet for the three O's in the title (Ｗ（ダブル） (, Ｗ（ダブル） ?) read as 'Double' and 555（ファイズ） (, 555（ファイズ） ?) read as 'Φ's/Phi's/Faiz') aside from an alternate spelling of the name of the main Kamen Rider: Ooz.

The creature designers are Yutaka Izubuchi, known for his work on the Lords in Kamen Rider Agito, and Tamotsu Shinohara, known for his work on the Mirror Monsters of Ryuki, the Orphnoch of Kamen Rider 555, and the Fangires of Kamen Rider Kiva. OOO is written by Yasuko Kobayashi, known for the screenplays of Seijuu Sentai Gingaman, Mirai Sentai Timeranger, Kamen Rider Ryuki, Den-O, and Samurai Sentai Shinkenger.

Kamen rider ooo episode 9