Basically, Its a wrestling manga disguised as a sentai series.
Its about a real alien invasion thats been reduced to a scripted event after the aliens executive, the big shots, have all been wiped out. The fodders are kept alive as a peace treaty, and they hold matches against the rangers for publicity sake.
MC is one of the fodders and he's tired of being a joke or a jobber. He decides to flip the script and is looking to enlist as a ranger.