I'm working on my own tokusatsu idea(separate from Super Sentai, Kamen Rilder, and Ultraman, but with similarities to the first two), even creating the hero Seidai no Genkotsu(Fist of Justice), and his evil counterpart but I cannot decide on a theme for the villains and kaijin.

Three Possibilities I have come up with are:

-Japanese and Chinese demons and mythology

-Mutant animal hybrids

-Bizarre aliens

Tell me which of these you prefer, or if you have a better idea, speak up.

EDIT:

I already chose a theme, based on input.

I will do them based on various yokai, though with a pseudo-mechanical armored appearance, because the theme will be yokai and masks.