Gridman Sigma (グリッドマンシグマ, Guriddoman Shiguma Gridman Sigma?) was the proposed ally of Gridman in a sequel series that was never completed or even aired. Sigma would have become the alter ego of Takeshi Todo, a reformed antagonist of the original series. Sigma would have fought a relative of Khan Digifier. In 2015 Gridman Sigma made his first public appearance in the anime short, Denkou Chojin Gridman: Boys-invent-great hero where he is finally partnered with Takeshi Todo.