This film is a combined remake of two tokusatsu (Japanese SPFX) hero series produced in the 1970s by Nippon Gendai and Senkosha; Shirubâ kamen (1971) and Super Robot Red Baron (1973), using new versions of the heroes from both series.
Goro Kirishima, the title hero of the 1972 tokusatsu Iron King, was shown at the end of the movie warning of the arrival of the Shiranui, foreshadowing a future crossover of more Senkosha heroes.
While the siblings are convinced that time travel will not change their own timeline and merely split off an alternate timeline, later events suggest (but do not prove) that they were incorrect.
There is only one Killgis alien active, all other antagonists are human-mimicking artificial lifeforms or robots. It is implied that once his job of altering Earth is complete, the rest of his people will travel to Earth.
The subtitles of the U.S. release have the time travelers arriving in 2013, contradicting other sources which place their arrival in 2015.