Yui Kanzaki

Yui Kanzaki is a Fictional Character in Kamen Rider Ryuki. She is the Sister of Shiro Kanzaki, the creator of the decks and she with Shiro is the partial creator of the Mirror World and it's Mirror Monsters. She spent most of the series opposing her brother on the Rider War.

Personality
Yui at heart is a young innocent girl who is caring to anyone she meets. However, this trait is what causes her the most trouble as a majority of the people around her are associates of the Rider War and only wish to use her to their advantage.

She hates fighting, as shown by the multiple times that she attempted to stop Shinji & Ren from fighting eachother.

History
Yui continued to live with her grandmother and while her grandmother was overseas on a trip, she met Ren somehow, although how this occurred is not specified in the series. Coincidentally, Ren was a Kamen Rider who had received his deck from Shiro at some point in time in Japan. Yui became somewhat of Ren's accomplice and would accompany him to fights where he would enter Mirror World and fight.

Time passed and eventually she also met Shinji who became Kamen Rider Ryuki. Her grandmother returned from her overseas trip and she began to help out at the cafe that her grandmother owned. She was kidnapped by Kamen Rider Scissors to use as bait to lure out Shiro but Ren was able to rescue her before that happened. Later, she went to Seimeiin University to inquire about her brother but everyone she asks was much less then helpful. After finding her brother in a Yearbook, Her past; which she previously had no memory of, began to reveal itself to her and she met Professor Ejima who worked alongside Shiro during the development of the decks. Ejima died in her arms but not before he told her that everything would have been fine if she had never existed.

She gets a Part-Time at ORE Journal while the Chief-Editor recovers.

After continually bothering Nakamura about her brother, he eventually gives in and provides her with a number of papers about Shiro. She learns about a Woman named Eri (who coincidentally again is Ren's Fiancée) who is in a coma at the hospital.

She is eventually kidnapped by Jun who uses her as bait to lure out Shinji & Ren into battle. Eventually, she manages to find a picture of her old house and goes with Tezuka to have a look but can't bring herself to go in.

Throughout the series, her past continues to unravel even further, she learns many things about her childhood, even finally remembering that she originally died as a child and that she really is the Mirror World equivalent.