|This article is about a/an machine and a villain in Kamen Rider Drive.|
- "I am Sigma. Ignition complete."
- ―Sigma Circular upon activation[src]
- "Unable...to defend... Unable...to execute plan.... I am...Sig-"
- ―Sigma Circular upon destruction[src]
After his escaping, Gold Drive and the Reaper Legion infiltrated the Special Defense Center headquarters, and placed Sigma under evolution process before the Kamen Riders (and later joined by the now-defected Roidmude generals Heart and Medic) would stop him from his plan on occurring the second Global Freeze.
Sigma's evolution was completed and activates the second Global Freeze just before Drive and Heart arrived to stop the machine. Sigma was destroyed by the combining finisher attacks of Drive Type Tridoron's Rider Kick and Heart Super Evolved's strength punch. With its destruction, the Global Freeze ends and all humans who were transformed into data were returned to normal.
- Heavy Acceleration
- As with all Roidmudes, Sigma Circular is capable of slowing down the movement of surrounding objects, including that of humans, with their unaffected consciousness aware of their impass during this time. One can be protected by the Heavy Acceleration effect by carrying Shift Cars or Signal Bikes on their person.
- Global Freeze
- Having absorbed the energies of all four Promised Numbers, Sigma Circular can generate a second Global Freeze. However, this time, not only it decelerate one's movements to the point where they are completely unable to move, it also digitizes humans into data and thus creating a new world under Banno's will. Even those who possess regular Shift Cars and Signal Bikes are also affected. Only Roidmudes who have achieved Super Evolution and Drive in Type Tridoron are shown to be able to move freely, however Medic was an exception, possibly due to Banno's reprogramming on her. While advanced Shift Cars like Shift Formula and Shift Dead Heat, which are able to resist Super Heavy Acceleration, allow users to move freely as well, these users are still affected by the digitization process.
- Barrier Generation
- Sigma can generate barriers as means of protection. However, the barrier it created must be plugged into a circuit which vulnerably can be deactivated.
- Stalagmite Generation
- Sigma can unleash teeth-like stalagmites for defense. It can also channel this power in a wider range.
- Despite not having legs and limbs, the machine still capable of moving around by levitation.
- Physic Explosion
- Sigma can create physic waves that explodes on contact.
- Laser Beam
- From its head, Sigma can release a small energy beam for offence.
- Sigma can move itself at a very high speed so much that it seems as it teleported.
- Energy Wave
- In a similar vein to the Promised Numbers, Sigma can launch a powerful purple shockwave.
- Energy Shield
- Sigma can create hexagonal shields for defense, able to resist the attack of Tridrop.
- An ability inherited by Banno, Sigma can generate red digital tentacles that capable of constricting its foes.
Behind the Scenes
- If the word "Sigma" were changed to the Greek letter ∑, its name ∑-Circular would resemble that of Mashin Chaser's E-Circular weapon.
- The giant teeth-like structures generated by the Sigma Circular have been seen in the show's opening since the very first episode.
- Kamen Rider Drive