Hideyuki Kagawa is the real identity of Alternative Zero, an imitation of the 13 Riders.
Prior to Kanzaki's experiment, Kagawa wandered into Room 401 at Seimeiin University 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, 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 Hajime Nakamura, with Kagawa eventually creating 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.
- Height: 190 cm
- Weight: 93 kg
- Maximum Running Speed: 100m/4.5s
- Sight: 20 km
- Hearing: 15 km
- Maximum Jump Height: 50m
- Punching Power: 15t (AP: 300)
- Kicking Power: 22.5t (AP: 450)
The Alternatives' sole contract monster, Psycorogue, resembling a humanoid cricket, had the ability to transform into a motorcycle named Psycoroader through the use of the Wheel Vent Advent Card and during the Alternatives' Final Vent Dead End. This Mirror Monster had an opposite color scheme to its corresponding Rider, having white armor with black accents. Its name is a portmanteau of the two words, psycho and koorogi, which is Japanese for "cricket".
Because they were designed by Kagawa and not Shiro Kanzaki, the Alternatives' Advent Cards differ from the ones used by the Kamen Riders. The terminals and images are printed crosswise, having the inscription 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.
Slash Visor: The Alternative system's card reader is mounted on the wielder's right forearm, with a female voice unlike the male voice used by the Kamen Riders's Visors. Unlike the regular Visors, the Alternatives swiped their Advent Cards across their Visors (much like the Rouzers used in Kamen Rider Blade), which burned up with jet-black flame and disappeared at the card's scanning.
- Advent (AP: 6500): Summons Psycorogue.
- Sword Vent (AP: 2000): Conjures the Slash Dagger.
- Accele Vent (AP: 2500): Increases the wielder's movement speed.
- Wheel Vent (AP: 4500): Transforms Psycorogue into Psycoroader.
- Final Vent (AP: 8000): Executes Dead End. While riding Psycoroader, the wielder spins out faster and faster until the bike is rammed into the opponent. Only Alternative Zero performed his Final Vent - the regular Alternative died before he could perform it.