As I said, there are various ways of doing that story without going military.
But, another that I thought of that they haven't done (And I think I'm probably out after this) is a character who uses his powers entirely for personal gain, but isn't necessarily evil, or on the villains' side. Although he's willing to screw over anyone & everyone to get what he wants, he still can't stand to see innocent people, or the other Rangers, placed in serious harm.
I think Kamen Rider's done that, at least once, & Sentai might have done it with certain monsters or villains, but I'm pretty sure Sentai has never gone there with a Ranger.