Gridman Sigma (グリッドマンシグマ Guriddoman Shiguma) is the younger brother of Gridman in a novel sequel series, Denkou Choujin Gridman: The Demon King's Counterattack. Sigma would have become the alter ego of Takeshi Todo, a reformed antagonist of the original series.
In 2015, Gridman Sigma made his first public appearance at the end of the anime short, Denkou Choujin Gridman: boys invent great hero.
Girdman Sigma was created both for the serial novel and Kazumitsu Akamatsu's desire to have both Thunder and King Gridman to fight side-by-side, hence his later form as King Gridman Sigma.
This plan was formulated back during the production of the original show. In the third quarter of the series, Takeshi Todo was meant to steal Gridman's data and become Khan Knight (カーンナイト Kān Naito), a rival character and Khan Digifier's servant, before redeeming himself as Grid Knight (グリッドナイト Guriddo Naito). Additionally, had the original plan taken place without the aforementioned production problems, Grid Knight would star in a sequel season. As revealed in an old magazine called Denkou Choujin Gridman 2: Great Determination! Great Monster Encyclopedia (電光超人 グリッドマン2 たいけつ!かいじゅうだいずかん Denkō Chōjin Guriddoman Ni Taiketsu! Kaijū Daizukan), there was a design of a second Gridman, who was themed after a European knight. Despite his near-identical appearance to Gridman save his head, Sigma is designed by anime Mecha designer Hideo Okamoto (岡本 英郎 Okamoto Hideo).
- First picture: Grid Knight - The white armor parts are inherited from Gridman and are meant to represent silver/metal.
- Second picture: Khan Knight - Aside from its black colored body, Khan Knight's undersuit is identical to Grid Knight's, having black and purple colors.
- Third to fifth pictures: Gridman II, the designs of a new Gridman, who bears resemblance to a knight.
Denkou Choujin Gridman: The Demon King's Counterattack
When Neo Khan Digifier, the younger brother of Khan Digifier attacks, Gridman and his own younger brother, Gridman Sigma appears. Choosing Takeshi Todo as his host, Sigma and his brother fight Neo Khan Digifier and his monster army. Their final opponent was Geist Digifier, which was Neo Khan Digifier's final form achieved by fusing with the souls of his defeated monsters.
Denkou Choujin Gridman: boys invent great hero
Takeshi appeared as an adult in the anime Gridman short. After watching the battles (or rather, relieving past memories) of the previous Gridman, Takeshi is granted the Acceptor by the light of several monitors and transforms by shouting 'ACCESS FLASH'. Transforming into Gridman Sigma to face monsters in the real world
- Height: Micro ~ 70 m
- Weight: 0 ~ 55,000 t
- Home World: Hyper World
- Maximum Flight Speed: Mach 30
- Via Gran Acceptor
- Grid Sigma Beam (グリッドシグマビーム Guriddo Shiguma Bīmu): Gridman Sigma's version of the original Grid Beam.
- Sigma Slash (シグマスラッシュ Shiguma Surasshu): Gridman Sigma conjures a blade of light to slash with.
- Sigma Punch (シグマパンチ Shiguma Panchi): A punching technique.
- Sigma Kick (シグマキック Shiguma Kikku): A side kick technique.
- Fixer Beam (フィクサービーム Fikusā Bīmu): Like Gridman, Sigma can also use the Fixer Beam.
- Double Grid Beam (ダブルグリッドビーム Daburu Guriddo Bīmu): Gridman and Gridman Sigma fire their signature finisher beams simultaneously.
- Lightning Rotation Slash (電光回転切り Denkō Kaiten Giri): Gridman and Gridman Sigma both slash the opponent.
- W Grid Punch (Wグリッドパンチ W Guriddo Panchi): Gridman and Gridman Sigma punch the opponent simultaneously.
- W Grid Kick (Wグリッドキック W Guriddo Kikku): Gridman and Gridman Sigma kick the opponent simultaneously. Gridman performs a flying kick while Sigma does a side kick.
King Gridman Sigma (キンググリッドマンシグマ Kingu Guriddoman Shiguma) is the fusion of Gridman Sigma and King Jet, the latter acting as its armor.
- Powers of King Gridman: The actual details are unknown, but it is presumed that he retains the same powers and armaments as King Gridman.
- King Sigma Beam (キングシグマビーム Kingu Shiguma Bīmu): Sigma's version of the King Grid Beam.
- Dragon Spiral (ドラゴンスパイラル Doragon Supairaru): Thunder Gridman and King Gridman Sigma fire energy beams which turn into three dragons that strike the opponent.
- Main article: Assist Weapons
In the same vein as Gridman, Sigma can also arm himself with Assist Weapons (アシストウェポン Ashisuto Uepon), specifically ones that his brother uses. Given that Khan Digifier had destroyed them in his final battle, it is more likely that they were recreated/repaired at some point of time.
- King Jet (キングジェット Kingu Jetto): A large aircraft made to be Dyna Fighter's support. Sigma combines with it to become King Gridman Sigma.
Denkou Choujin Gridman: boys invent great hero
- Masaya Obi, the actor of Naoto Sho has Gridman Sigma's version of Acceptor. Whether it was the original prop or his own custom made is unknown.
- Sigma's blue design would be later used in many other Ultras.
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