This term came from the Japanese battle cry tennMheika banzai (Y)v[NNks, transl. "long live His Majesty the Emperor"), and was shortened to banzai, specifically referring to the tactic used by the Imperial Japanese Army during the Pacific War.
Spain was nominally neutral during World War II, though under General Franco's far-right Nationalist regime it was politically aligned with Nazi Germany. Spain did not actually join the Axis side but it collaborated with the Nazis in many areas.