Get started on the Veri-Tech Valkyrie or Alpha.
HA!
The problem is that Japan needs a pure air superiority fighter then a multirole aircraft. That said, in the end the F-35 is too good for them to pass up. Even though it’s expensive, it’s still off the shelf for them. It’s stealth makes up for a lot of it’s short comings along with it’s sensors and electronic warfare capabilities.