You have your answer.
Nika is the human who ate the first ever DF. The fruit bloomed on a certain tree because the enslaved people prayed for a savior, and their dead souls were absorbed by the tree, like we've seen in Skypeia, and ultimately "condensed" into the fruit.
It wasn't the Nika fruit. It was a fruit to bend reality. After Nika consumed it and became the much-awaited savior, the fruit was renamed after him.
I actually believe Nika himself was one of the enslaved people.
My theory is that the people that came from the moon terraformed the earth and enslaved its inhabitants, similar to how the Gorosei have warrior god titles I believe these moon people had something similar where each “God” was just responsible for a project.
Earth God oversees the terraforming process of the earth, Forrest God is responsible for planting these magical trees, Rain God is responsible for raising the sea levels and the Sun God was like the Science God Saturn overseeing the scientists responsible for harvesting the endless flame(power source).
I believe that the Sun God betrayed the other Gods and their “king”, the very first Imu/Devil and upon doing so was killed but not before giving his blessings to a slave human boy named “Monkey” which he befriended by giving him the very first fruit harvested from the magical trees which he intended to eat himself but never managed to.
The Monkey Boy inherits the title of the Sun God by those who were saved and becomes the first Sun God Nika; wins against the demon in a Great War that scarred the earth forever and establishing the ancient kingdom becoming its first king and the Monkey dynasty.