Kashiwa Reysol is one of the oldest clubs in the J.League, ranking behind only Sanfrecce in terms of continuous participation in a nationwide league of some sort. The team got its start in 1940, as the company soccer team of Hitachi. Hitach FC was fairly successful during the mid-1970s, winning several Emperor's Cup and League Championships and contributing several players to the Japan National Team. In 1992, the name of the team was changed to Kashiwa Reysol, in preparation for J.League membership.
Reysol is a pseudo-Portuguese word created by merging the words "Rei" (king) and "Sol" (sun). While this name is a thinly disguised plug for the parent company, Hitachi, at least the corporate sponsors have refrained from interference in management, unlike some other teams that tried to ignore the J.League's rules on independent operation. The mascot, named "Rey," is an even more direct reference to Hitachi, which literally means "Standing Sun": A cartoon depiction of the sun god, standing at attention.