Shizuka Shiroyama is Saeba's personal secretary. She was the human identity of the Space Ironman Skydain.
Skydain, Groundain, and Black Knight were created by Professor Blink; but the Kyodain went rogue and attacked the professor. The professor proceeded to seal their power in the satellite they were in, forcing the Kyodain to assume weak human forms.
Under the guise of the clumsy assistant to Harumi Saeba (her brother's guise), Shizuka Shiroyama of OSTO Legacy, Skydain plotted with her brother to use the Kamen Rider Club to regain their powers and take over XVII. When their plan succeeded, the Kyodain began their genocide attack with XVII but Kamen Rider Fourze Cosmic States managed to foil the plot with his warp drive ability.
Enraged, the Kyodain fought him and Kamen Rider Meteor. While at first having the advantage, Fourze gained the Fusion Switch and after a long battle destroyed them with the States' Limit Break.
- Skydain is an inversion of a classic tokusatsu superhero, Skyzel, one of the Space Iron Men Kyodain from the 1976 TV series of the same name made by Kamen Rider creator Shotaro Ishinomori. Unlike Skyzel who is heroic and a "male gender" robot, Skydain is female and pure evil as she cares nothing for the lives of those on Earth. She does however exhibit some of the same abilities as her original counterpart.
- Kamen Rider Fourze, her enemy, loosely resembles Skyzel in design, albeit with an astronaut/rocket motif instead of a jet.
- Skydain's human form is portrayed by Ayumi Kinoshita, who is known by Super Sentai fans for playing the role of Marika "Jasmine" Reimon aka DekaYellow on Tokusou Sentai Dekaranger.