Following the events of Kamen Rider Den-O, Negataros 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 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 in Hyper Hobby Magazine. The story is a retelling of the events of Climax Deka featuring Negataros traveling to April 3, 1971, to team up with the Shocker organization and combating 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, Ax Form or Gun Form, Nega Den-O can use their equivalent Nega DenGasher weapon modes in battle.
- Rider height: 180 cm
- Rider weight: 95 kg
- Ability perimeters:
- Punching power: 7t
- Kicking power: 8t
- Maximum jump height: 38m
- Maximum running speed: 100m/4.8s
Nega Form 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.
Nega Den-O Belt
The Nega Den-O Belt is Kamen Rider Nega Den-O's henshin belt. It is affixed with a device known as the SetTouch in the Terminal Buckle, which can read a Rider Pass 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. Unlike the voice on the original Den-O belt, this one a has distorted voice.
The Machine Nega Den-Bird 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 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 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.
- Kamen Ride: Nega Den-O: A Rider Card containing the power of Kamen Rider Nega Den-O. Used by Diend to summon Kamen Rider Nega Den-O. This card is used by Diend in Kamen Rider Battle: Ganbaride.