[DigitalConrad]

As a running joke, I have Super Sentai Poweranger for the 40th series. All the rangers would have popular Japanese names for the time and the 6th ranger will be an American with a name like Gregory Johnson or something.

As an actual theme, Metal Sentai Rock-uger where all the rangers are different styles of Rock/Metal Music and they fight against a villain known only as The Man. It could have a villain naming theme a'la Goseiger/Jojo's Bizarre Adventure where they're named after some big name music acts.

Red: Heavy Metal
Blue: Speed Metal
Yellow: Power Metal
Black: Alt. Metal
Pink: Death Metal

6th Ranger: Nu Metal

I don't know much about Metal music, this was just a little idea a few friends of mine had a while back.