Following the events of Kamen Rider Den-O, Negataros (ネガタロス Negatarosu?) and a select few Imagin are stray Imagin who evaded the fate of the other evil Imagin when Kai ceased to exist in the final episode. Soon afterward, he steals an extra Rider Pass before arriving to restore the future where the Imagin exist by recruiting mobsters and members of the Fangire Race to his aid. In Climax Deka, Negataros has to deal with both the DenLiner Police (デンライナー署 Denrainā Sho?) led by Ryotaro Nogami, an inside man in the form of Yuto Sakurai, further worsened by the brief meddling of Wataru Kurenai.
In the end, Negataros' plan is foiled and his armor is destroyed by the Double Boistous Kick & Darkness Moon Break of Kiva & Den-O Climax Form before he finally meets his end in battle against the DenLiner, the ZeroLiner and Castle Doran.
Negataros is also featured prominently in the S.I.C. Hero Saga (S.I.C.ヒーローサーガ Esu Ai Shī Hīrō Sāga?) in Hyper Hobby Magazine. The story is a retelling of the events of Climax Deka featuring Negataros travelling to April 3, 1971, to team up with the Shocker organization and combatting Den-O and the Tarōs along the way.
By swiping a Rider Pass across the SetTouch, Negataros is able to transform into Nega Den-O. Unlike Den-O though, because the user is an Imagin, Nega Den-O bypasses the Plat Form to assume his only fighting form. Though he has no other fighting forms equivalent to Rod Form, Axe Form or Gun Form, Nega Den-O can use their equivalent Nega DenGasher weapon modes in battle.
- Rider height: 180cm
- Rider weight: 95kg
- Ability perimeters:
- Punching power: 7t
- Kicking power: 8t
Nega Form (ネガフォーム Nega Fōmu?) is Nega Den-O's only fighting form. It is visually similar to Den-O Sword Form, but is a deep shade of purple as opposed to red and has teal tribal markings all over the armor. As with Den-O Sword Form, it is based on the story of Momotarō, the Peach Boy.
The armor met its end at the hands of Den-O Climax Form & Kiva's Double Rider Kick.
The Den-O Belt (デンオウベルト Den'ō Beruto?) is Kamen Rider Nega Den-O's henshin belt. It is affixed with a device known as the SetTouch (セタッチ Setacchi?) in the Terminal Buckle (ターミナルバックル Tāminaru Bakkuru?), which can read a Rider Pass (ライダーパス Raidā Pasu?) and the Imagin contained on it. When the Rider Pass is swiped across the SetTouch, a transformation can occur. The belt has four buttons (red, blue, yellow, purple), but these are not used as the SetTouch is already a shade of red. It is also used to activate the primary finisher, Full Charge (フルチャージ Furu Chāji?). Unlike the voice on the original Den-O belt, this version has a distorted voice.
The Machine Nega Den-Bird (マシンネガデンバード Mashin Nega Denbādo?) is Nega Den-O's bike that is able to launch from the Nega DenLiner. It is only seen in the Nega DenLiner when Negataros is piloting it. As with Machine Den-Bird, Machine Nega Den-Bird is based on a Honda XR250.
The Combination Armament Nega DenGasher (連結武装ネガデンガッシャー Renketsu Busō Nega Dengasshā?) is modeled after a High-speed rail and is Nega Den-O's primary weapon. The Nega DenGasher is composed of four separate parts that, when not in use, are attached to the Den-O Belt. As with Den-O, Nega Den-O can use the Nega DenGasher in all four of its combinations while in Nega Form. And as with Nega Den-O's armor, the Nega DenGasher's blade has tribal markings.
The Nega DenLiner (ネガデンライナー Nega Denrainā?) is Nega Den-O's transportation system, a Shinkansen (bullet train), similar to DenLiner Gouka in appearance, but as in the style of Nega Den-O, it has tribal markings all over it. In comparison to DenLiner Gouka, the Nega DenLiner's second to fourth cars open up to reveal Gigandeaths. The first car is a laser cannon, the second holds two Gigandeath Hades that fire lasers, the third car holds a small Gigandeath Hell that launches bombs, and the fourth car holds Gigandeath Heaven.