Fujishiro, we don't even know what a Nika is lmfao. Let's be real.
And at that the end of the day, all Luffy did was awaken some mythical zoan related to Nika. He isn't actually Nika, unless we assume that Sengoku is actually the Buddha. Legitmatley, there's nothing Luffy could to that would make Imu care about him if Imu let Xebec go after xebec invaded his castle. That's actually crazy