Toei worked with Marvel on the Japanese Spiderman series, and then they started working together on a Japanese TV show loosely based on Captain America (Captain Japan?!). As work continued they started bringing in other characters representing other countries and somehow ended up with Battle Fever J. It was a co-production that (at least on paper) was based on Marvel source material, so Toei and Marvel co-owned it. The copyright information in the credits for the next two series also included Marvel's name, but it isn't thought that they actually had any involvement in it. It was just that they had a three series co-production contract (Spiderman, Fever, Denji) and because Sun Vulcan was a sequel to Denjiman they thew the same copyright info on.
They renamed him Battle Japan and he became the red ranger for Battle Fever J. Nothing else came of it though AFAIK. The Power Rangers wikia reckons that Queen Hedrian (from Denjiman and Sun Vulcan) is based on the Thor villainess Hela, but that seems to me more like someone spotting vague similarities and calling them links rather than anything concrete.
