>>283192091
Just showing clips to some old tokusatsu goes a long way.
Ultraseven, which Big O's OP is clearly imitating:
https://www.youtube.com/watch?v=iCuz2D7br78
And some MADs of Red Baron and its sequel Mach Baron, which are design influences. Mach Baron especially, with the heavy forearms.
https://www.youtube.com/watch?v=l0bHSvARr34
https://www.youtube.com/watch?v=o0CoctI8XAo