The trains were built jointly by
Hitachi and
Nippon Sharyo. The trains were developed to accommodate the increasing number of long-distance commuters along the
Tōkaidō Main Line and to provide seated services and express services using the parallel freight lines. The bilevel designs are based on the Green car of the
211 series and the prototype Kuha 415-1901 of the
415 series. Excluding the leading cars, all cars are bilevel with ordinary-seating cars fitting at most 120 passengers. A set can carry up to 1010 passengers. As the train was intended to be operated only on the warmer Tōkaidō Main Line, it was not designed to withstand the cold or snow. As such, the train operated on the
Chūō Main Line only between spring and autumn. ==Formation==