|Name: Hideyuki Kagawa|
|Designation: Alternative Zero|
|Weapons: Slash Visor|
|Advent Cards: Advent, Sword Vent, Accele Vent, Wheel Vent, Final Vent|
|Contract Beast: Psycorogue|
|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. 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.