Yui Kanzaki
A 19 year old woman who had been aiding Ren prior to the series. Yui's purpose for joining Ren is to find clues about her long lost brother Shiro. After Yui and Shiro were separated as children, Yui grew up in Aunt Sanako's Tea House, Atori. Yui can walk safely in the Mirror World, though she does collapse after a while. She can control the Mirror Monsters and later, began to pixelate in the real world. When she was 7, she fell out of the chair while she was drawing. When Shiro panicked and called for their parents, they ignored him and left the door locked. Yui's mirror reflection offered to give her a new life, but explained to Shiro that this life would run out when Yui became twenty. Yui remembers almost nothing about their parents, who were killed when the house caught fight after the first mirror-breach. Yui, once she learned the price of her life, could not bear that her life was at the cost of so many others. She then was determined to make herself disappear. She could still have been saved, but in the end of the TV series, it was Yui's wish that came true. When Shiro would have started the whole sequence of time again, she took them out of the equation. Shiro and Yui Kanzaki died in 1989. They moved into the Mirror World, to live with their adult Mirror World reflections.
Shiro Kanzaki
He is Yui's beloved older brother. Yui used to be made fun of by kids because of her belief of mirror monsters, and he protected her. When their parents died because of a fire caused by a monster breach, Shiro was taken in by their mother's sister in America. He was dragged in into the taxi. Before his parents died, Yui died and he accepted for her to live thanks to her mirror duplicate until she became 20. He swore he'd save her. He became a scientific genius in America, creating the Kamen Rider Card Deck. He opened the Mirror World and it killed him. I suspect that the one we see most of the time is Shiro Kanzaki's Mirror World self. Shiro was determined to save Yui, knowing what would happen to her. Though thought to be cruel for manipulating the Riders and pushing them to fight, Kanzaki's intent for the Rider war is for his sister's life. The Riders hear his voice in the depths of their minds. He stirs the violence in their nature, calls them to fight. Shinji resists on a subconscious level, because Kanzaki did not choose him to be a Rider. In the finale of the TV series, Shiro would have started the whole sequence of time again, she took them out of the equation. Shiro and Yui Kanzaki died in 1989. They moved into the Mirror World, to live with their adult Mirror World reflections.
Sanako Kanzaki
Yui and Shiro's father's sister, Sanako owns the Tea House, Atori. Sanako considers herself to be a wise woman and says that her intuition is never wrong. Aunt Sanako is a bit of an eccentric. She's currently saving up money for a trip to the Amazon. She loves Yui tremendously. She took an immediate dislike for the hard as nails Ren, but welcomed the clumsy Shinji with open arms. And since he was looking for a place to stay, she figured he could move in there and work there to be around in order to dislodge Yui from Ren. Unfortunately Shinji was clumsy so Ren stepped right in and was impeccable employee. Grudgingly, Sanako decided to keep them both.
Reiko Momoi
Reiko Momoi is 24 and she's a dedicated journalist at ORE Journal. She pursues the vanished people with tenacity, even willing to consider the mirrors were related. She even went after Asakura and got suckered by him into bringingin his baby brother. She is determinedly ignoring Kitaoka's attempts to try to date her because he would alienate her. She pursued the disappearing people and eventually discovered their connection with Shiro Kanzaki, including his connection with the monsters and the Mirror World. Later on, she discovered that Shinji was a Kamen Rider. Megumi and Shimada begun pushing Reiko to accept his requests for dates, but were sworn to secrecy about his cancer.
Daisuke Okubo
Chief Editor of the Open Resource Evolution Journal. He is 36 and lives to be unconventional. He likes to be surrounded by the few eccentrics he has hired. He encourages them, basically lets them go their own way. He had the ignoble experience of having Ore Journal briefly taken over by that snappy young computer hacker, Jun Shibaura. But he survived the experience with dignity merely ruffled.
Nanako Shimada
Nanako Shimada, 23 years-old systems engineer and web-site designer of the ORE Journal. She's quite talented, adores computers and gets along better with them than with humans. She also has a slight crush on Shinji.
Megumi Asano
Formerly Kitaoka's ex-secretary, she returned into his life claiming that the two of them were to be married. He almost got married to her because she lied about dying. Megumi is a strong individual and quite capable in a fight, however she is quite ditzy, which was why Kitaoka had fired her. She would later be hired by Daisuke as a journalist for ORE. She once witnessed Shinji walk out of a glass window once. She makes Shimada upset at first but they appear to be becoming friends. Shimada and Megumi successfully managed to drag Kitaoka and Goro off for an evening of drunken Karaoke. She wants to be a journalist.
A former professor at Seimeiin University, he was the one who help Kanzaki perform the experiment that resulted with Eri's coma. Since then, Ejima left the university and wandered the city with a Seal card in hand to protect himself from the Mirror Monsters. But once he loses the card, Ejima ran back to his lab to plea Kanzaki to help him as he's attacked by a Terabiter. Though saved from the monster, Ejima dies of a heart attack as he sees Yui and laments that she should have never been born.
Eri Ogawa
Eri Ogawa, Ren's fiance was in a coma since about August 2001. Ren eventually was able to save her at the end of it all.
Series:  Kamen Rider Ryuki