Japan, turned down in its efforts to buy the U.S. F-22, is planning to spend half a billion dollars to develop its own stealthy fighter. Maybe. Japan is eager to find a modern fighter to replace its 118 F-4 and 178 F-15 aircraft. With China and Russia putting more new fighters into service, Japan sees a threat. The U.S. F-35 is not the solution, and the Eurofighter and Rafle have not made the cut either.
Japan has built its own fighters recently. In the 1990s, it designed and built a modified version of the U.S. F-16. That proved to be a financial disaster, with each of the 22 ton F-2s cost $120 million. While a bit larger, and somewhat more capable, than contemporary F-16s, the cost was about four times as much. Only 98 were built, rather than the 141 originally planned. The aircraft entered service seven years ago.
A stealthy "F-3" would still require a lot of American technology. Japan builds fighter jet engines under license, and could probably get licenses to enough of that technology so that it could design an engine for its new fighter. Japan is already a leader in developing and manufacturing aircraft electronics. But a major problem remains the high costs of developing and building weapons inside Japan (where wage and benefits costs are quite high).