Imu might have been the original Nika, but Joyboy tried to steal his power, the original mother flamme. For the Ancient Kingdom. What led to JB's death and the conflict. Imu Spent 800 years trying to fix it.. and even created a new "forbidden sun" version of it.

It could be a potential scenario too, what are you thinking of this version of the story ?? It would Make Sense.

If Imu was, indeed, the original owner of the fruit, or Nika, it would be Logic to admit that the World Government was created After the events of the great War and the Void Century no ??

Like, the Motherflamme was Stolen from Imu, Imu killed JBoy for his sin and as a result of that loss, Imu loses the fruit, the Nika Fruit and become Void. An entity is created from nothingness. The World was Plunged INTO darkness, Nika becomes the Void.

And, the creation of new Devil fruits comes right After this event. But, they might have existed long before. Imu was l'EFT with no choiced, but with the Only One choiced : to eat the forbidden Sun, the Akuma no mi, empowered by the mother flamme. The forbidden fruit.

This is the Only way to recapture his own soul, because Nika is an eternal being. At least, his Body was special. This is why Luffy is Not Joyboy, because he is Not Nika. But, he possesses the fruit.

And, Imu, a.k.a the first Nika, is Now like an Android, or a Seraphim whom Received a golden heart, or an artificial one. And, his blood is still special, this is where he Gets his strength from and why he is so powerful and Stronger than anyone else yet.

Like, they originally where Strangers to the other, Imu, Joyboy, Davy Jones, but they decided on purpose to create an alliance. And, someone betrayed an other.