Japan Domestic Airlines Co., Ltd.(日本国内航空,Nihon Kokunai Kōkū?) was the predecessor of Japan Air System.
On April 15, 1964, Nittoh Aviation Co., Ltd. (NAL) (日東航空,Nittō Kōkū?), Fuji Airlines Co., Ltd. (FAL) (富士航空,Fuji Kōkū?), and North Japan Airlines Co., Ltd. (NJA) (北日本航空,Kita Nihon Kōkū?) merged to form Japan Domestic Airlines. On May 15, 1971, the airline merged with Toa Airways to form Toa Domestic Airlines; on April 1, 1988 the merged airline renamed itself to Japan Air System. Japan Air System merged into Japan Airlines in the early 2000s.
Nearly all of the aircraft used in the Japan Domestic Airlines fleet were consisted of NAMC YS-11s. Both airlines had a similar color scheme from the beginning, usually blue and white, or with a blue tail. Japan Domestic Airlines focused mostly on mainland to island flights, while Toa Japanese Airlines focused on more domestic mainland flight plans and services.