Dark Yuki or also known as Gemini Zodiarts was the evil side of Yuki Jojima, she was also one of the Horoscopes, and a major antagonist in Kamen Rider Fourze.
Kamen Rider Fourze
Dark Yuki was created when Libra and Leo Zodiarts forced Yuki to activate his Zodiarts Switch thus causing his dark emotions that aroused Gemini Zodiarts. She then woke up inside Yuki's body and soon started vandalizing graffiti among other cheating things. After that Gentaro and then Kamen Rider Club realized that they soon saw two different Yuki. And they discovered that they soon saw two different Yuki. And they discovered that they parted after Libra and Leo Zodiarts forced activated the Zodiarts Switch, Gemini Zodiarts fought against Gentaro in the end she was defeated when Fourze used Rider Super Galaxy Finish.