Ever since Japan removed the military export ban we had implemented for decades, we can sell air units, land units, to naval units to partners. I don't see why there should be any bias here, I mean, the Russian Federation sells Sukhois to China and Vietnam, while knowing both are rivals. Russia sells submarines to Vietnam, and at the same time sells anti-submarine air units to China. All is fair in military sales, my dear. Why should Japan have inhibitions?
Come on, even the United States sells F-16s to Pakistan and to India, knowing that both are rival nations. The same in regards to selling F16s to Turkey and Greece -- while knowing they are both rivals.