These 20 2-8-2 locomotives, which were delivered by Baldwin to the Nippon Railway in 1897, gave this wheel arrangement the name “Mikado”. Their manufacturer called them type 12-30 1/4 E, while their designation on the railway was originally Bt4/6. To burn low-grade coal from the Joban coal fields, they needed a large grate. So a trailing axle was added, above which a wide firebox was mounted. With small drivers of only 45 inches and cylinders which measured 18.5 by 24 inches, they were the most powerful locomotives in Japan at this time.

Their main task was to haul freight trains on the Joban line, located on the east coast of Honshū, north of Tokyo. In 1901 and 1902, five locomotives received a new boiler with a Wootten firebox. With this the firebox heating surface increased from 9.3 to 11.9 square meters, while the tube heating surface decreased from 197.8 to 142.4 square meters. From 1909, the JGR numbered them 9700 to 9719. They were used until 1922.