Despite the over budget, and overhyped F-35, there are many videos displaying its capabilities that it's more than capable and Japan has an urgent need for stealth aircraft, sooner than later. Mitsubishi had plans to make a native fighter to replace the F-2 (similar to the Fighting Falcon) called the Shinshin X-2, or experimental. It remains DOA and with the order of these nearly 100 F-35s, it will more than likely never come to fruition.
Japan may acquire a considerably more number of F 35s. It is to be noted that it already has 42 conventional-takeoff F-35A on order at a cost of around $7 billion, to replace the 73 aging F-4E fighters.
The latest development is significant development as it comes at a time when Japan has become increasingly uneasy with Chinese military provocations.