In order to be able to transport large numbers of people efficiently during the war, electric railcars that were simple and cheap to produce were developed. These vehicles, later named Class 63 by the JNR, were originally developed as power cars, trailers and driving trailers with the designations MoHa 63, SaHa 78 and KuHa 79. Their initial purpose was primarily to transport workers to the armaments industry. With four doors on each side, boarding and alighting passengers could be handled quickly, and thanks to an easy-to-manufacture steel car body, manufacturing could be sped up. They were the beginning of a long series of commuter railcars, which, with many doors and a high proportion of standing room, were able to cope with the immense number of passengers in the Japanese metropolitan areas.

Due to the course of the war, only relatively few examples were built before the end of the war. Immediately afterwards, production continued on a larger scale in order to cope with the sharp increase in passenger numbers. Kawasaki Heavy Industries now manufactured railcars with an aluminum car body, as this was now easier to obtain. These also featured luggage racks and upholstered seats. Of the 688 cars built in total, those built during the war wore out after just a few years because the manufacturing quality was very poor. The aluminum cars also had to combat corrosion, which could also lead to short circuits and fires. With the class 72, an improved derivative was created and ultimately almost all vehicles from the class 63 were converted to the class 72.