Hideyuki Kagawa

Kamen Rider Alternative and Alternative Zero were not Kamen Riders like the others, they were two men that created their own decks, so they weren't let's say, 'official' or 'original' ones that Shiro Kanzaki (Yui's brother) made.

Hideyuki Kagawa
Prior to Kanzaki's experiment, Professor Hideyuki Kagawa wandered into Room 401 one day and happened to see Shiro Kanzaki's notebook lying on the floor. He scooped it up, opened it and gave every intriguing page a once-over glance before Kanzaki snatched it from him. However, Professor Kagawa had photographic memory and remembered what he had read. After learning the severe nature of Kanzaki's experiments, Kagawa began to duplicate Kanzaki's work in order to close the Mirror World. To that end, he formed a relationship with Satoru Tojo and Nakamura. Kagawa eventually created the Alternative decks.

Kagawa was a married man, with a young son named Yuuta. Though he deeply loved both his wife and son, he did not let Kanzaki's threat to their lives deter him from his course to close the Mirror World. Unfortunately, he died for it at the hands of Satoru, who did it based on the man's word that a 'hero must sacrifice the one they love.' Satoru would come to regret his deed in the name of heroism. Unlike the other Advent Cards, Alternative and Alternative Zero's cards are different in appearance; the terminals and images are printed crosswise unlike the original Advent cards that have theirs printed lengthwise, and are given the title, "Alternative Advent Card Alchemy System" at the back. Also, there are green characters on the cards, which may give information to the Visor on what kind of card is swiped. Because their equipment was designed by themselves, the V-Buckles' and Card Decks' appearances were different from the other Riders.

Fictional character biography (Alternative Zero)
Ability Perimeters
 * Height: 190cm
 * Weight: 93kg
 * Maximum Running Speed: 100m/4.5s
 * Sight: 20km
 * Hearing: 15km
 * Maximum Jump Height: 50m
 * Punching Power: 300AP
 * Kicking Power: 450AP

Contract Monster
The Alternative's sole contract monster Psycorogue resembling a humanoid cricket, Psycorogue could transform into a motorcycle called the Psycoroader. This contract monster has white armor with black accents while Alternative Zero and Alternative's armor were black with white accents, contrary to other Riders whose armor was similar with their contract monster. Its name is a portmanteau of the two words, psycho and koorogi, which is cricket in Japanese. The Final Vent move Dead End transforms Psycorogue into a motorcycle then Alternative and motorcycle spin-out faster and faster until they ram into the opponent.

Psycorogue survived it's master when controlled by Yui. It was weakened by Ryuki's Drag Claw Fire and then destroyed by Knight's Hishou Zan.

Advent Cards
Unlike the other Advent Cards, Alternative and Alternative Zero's cards are different in appearance; the terminals and images are printed crosswise unlike the original Advent cards that have theirs printed lengthwise, and are given the title, "Alternative Advent Card Alchemy System" at the back. Also, there are green characters on the cards, which may give information to the Visor on what kind of card is swiped. Because their equipment was designed by themselves, the V-Buckles' and Card Decks' appearances were different from the other Riders.

Slash Visor : The card reader of Alternative Zero/Alternative was mounted on his right forearm. The visor voice was different from those of real Riders, the voice was female. Another difference was how the cards were used with the visor. The cards were swiped (similar to the rousers in Kamen Rider Blade), which burned up with jet-black flame and disappeared when the card was vented.
 * Advent (AP: 6500): Summons Psycorogue.
 * Sword Vent (AP: 2000): Conjures a lance.
 * Accele Vent (AP: 2500): Increases Alternative's movement speed.
 * Wheel Vent (AP: 4500): Transforms Psycorogue into Psycoroader
 * Final Vent (AP: 8000): Executes Dead End. Psycorogue transforms into a motorcycle, then Alternative and motorcycle spin-out faster and faster until they ram into the opponent. Only Alternative Zero performed his Final Vent. Alternative was killed before performing it.

Links

 * Kamen Rider Ryuki (DVD)
 * Kamen Rider Ryuki @ TV Asahi
 * Kamen Rider Ryuuki Spoiler Page