A total of 25 Class EF63 locomotives were built between 1962 and 1976 exclusively for use as bankers (U.S. "helpers" or "pushers") on the steeply-graded Usui Pass section of the Shinetsu Main Line between Yokokawa and Karuizawa.

The class was equipped with a number of special safety features to cope with the unique conditions of operating on the 66.7‰, 6.67 % gradient of the Usui Pass.

The entire class was based at Yokokawa depot, and they were always used in pairs at the Yokokawa end of trains travelling in both directions, and were capable of operating in multiple with Class EF62 locomotives and a wide range of EMU types (including 115, 185, 189, 489 series) – hence the impressive array of jumper cables and connectors on the Karuizawa ends of the locos.

The closure of the Yokokawa to Karuizawa section of the Shinetsu Main Line in September 1997 coinciding with the opening of the new Nagano Shinkansen marked the end of the careers of the EF63 locomotives.

Source:[2] EF63 24 and 25 are currently used to provide driver training sessions to members of the public at the Usui Pass Railway Heritage Park on a short stretch of track electrified at 750 V DC (rather than the normal 1,500 V).