Work started in 1980s under the FS-X program, and began in earnest with a memorandum of understanding between Japan and the United States. It would lead to a new fighter based on the General Dynamics (post 1993, Lockheed Martin) F-16 Fighting Falcon, and in particular the F-16 Agile Falcon proposal. Lockheed Martin and Mitsubishi Heavy Industries co-developed and co-produce the aircraft, the company is a major subcontractor to Mitsubishi, some of the early developmental work was actually under General Dynamics, who sold its aircraft division to LM in 1993. It is essentially an execution of the F-16 Agile Falcon proposal- a late 1980s plan for an enlarged F-16 which was passed over in the U.S. in favor of an all-new fighter program (Joint Strike Fighter). The F-2 used the wing design of the F-16 Agile Falcon, but much of the electronics were further updated to 1990s standards. The overall concept of the enlarged F-16 by General Dynamics was intended as a cheap counter to the then emerging threat of Su-27/MiG-29.
more info at
http://en.wikipedia.org/wiki/Mitsubishi_F-2
Thanks for the info & link.