A different ending was originally planned where Nelson and his goons kidnap Shinji rather than tie him up. They then head for Rolisica via Nelson's private plane, but the plane crashes in Kyushu and Chujo. Senchiro and the police track them to a cave where Shinji breaks free and takes the case containing the fairies. Shinji then opens the case and the fairies telepathically contact Mothra who flies to where the action was. In a final confrontation with Nelson and his goons, Mothra ends up killing them and flying back to Infant Island with the fairies.
Jerry Itô's slow stilted delivery of his Japanese dialog fit his character as a foreigner speaking Japanese. This was not an intentional part of his performance. At the time this was made, Jerry Ito had been studying the Japanese language for over six months and was not completely fluent.
For years it was thought that Rolisica was actually based on the United States. However, it was revealed years later that it was based on both the United States and the Soviet Union. In fact, the name of the nation of Rolisica is a hybrid of Russia and America. The name of the country originally was going to be Roshirica. Also, the Rolisican flag is a hybrid of the American "Stars and Stripes" and the Russian "Hammer and Sickle".