If y’all are familiar with Kamen Rider and/or Kamen Rider Build, you prolly know that the main character, Sento, uses the power of math and physics to henshin! into his various forms.
He starts off by shaking his bottles:
Which causes math equations to appear from the sides. Sento is also a physicist, btw.
Heck, even his finishing move is math-related.
That concludes my wild theory on why Sigma could be a Kamen Rider, I made this for fun so please offer your feedback on it. 
Oh, and if you guys have heard of Kamen Rider, I love you.
Cheers,
~ PyroPanda