Tanaka is a Dark Rider that appears in Kamen Rider Decade.
An A.R. version of Alternative is an evil Rider associated with the Dark Riders who assumed the guise of the Negatives World counterpart of the real Tanaka, Natsumi Hikari's high school teacher. Though ordered by Otoya Kurenai (A.R. World) to keep an eye on Natsumi rather than kill her, he intentionally decides to attack Natsumi, resulting in Dark Kiva beating him merciless. Alternative is then later destroyed by Kamen Rider Diend.
- Height: 195 cm
- Weight: 98 kg
- Maximum Running Speed: 100m/4.5s
- Sight: 20 km
- Hearing: 15 km
- Maximum Jump Height: 50m
- Punching Power: 300AP
- Kicking Power: 450AP
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 Ryuki 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. 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.
The Alternative's 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".