A political thought: police corruption in fiction is nothing new, but as an American, I just could not help but link the basic premise with the ongoing and increasing attention to the very real and very dangerous police corruption and brutality in the real world. It's a first to have corrupt SPD for Dekaranger I think, though Power Rangers: SPD did this 10 years ago; and even if it's not the first, they definitely brought it back to the forefront. Yet in both shows, it brings that concept to child audiences. Fiction is often a reflection of the times, though I'm more than certain that it was neither Sentai nor PR's intention to do that. Even then, A-Squad was a landmark in that they were America's first willingly corrupt Rangers.
I'm sure I'm projecting here, and I've no idea what conversations are going on about Japan's law enforcement (if any), but still, that police corruption is such a common trope that it's in kid shows now is fairly alarming. Tropes don't come from vacuums, they come from experience and consumption. Though, of course, the case can be made that this movie was made for older audiences because of the 10 year nostalgia (that and there's an actual blood splash!)