[VoidinToku]

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Originally Posted by macblo

Its the only one of the big three Tokusatsu that regularly have humans as their primary villains rather then non humans. While they obviously still fight monsters and other none humans, humans are more often then not extremely important, if not the primary, villains. Kamen Rider in general seems a lot less afraid in general to show the dark side of humanity. Its kind of interesting how Kamen Rider has retained its darker elements long after sentai has abandoned them. That later time slot makes all the difference man...

Kamen rider's powers usually originate from the villains one way or another, so riders are seen as monsters themselves in their respective series. So it wouldn't hurt to have them battle other human transforming monsters. Modern rider series tend to depict the human guest of the week being the monster of the week either through transforming from humans to monsters or vice-versa. Sentai only retain using the enforcer and final boss having a human appearance after 40 years. Overall, sentai usually deals with alien invasions while riders deal with more one on one human's problems.