According to me Nika was a Warrior Leader/God of a alliance of Countries(Wano, Zou and Ryougukyou for exemple) who was at war before with the Ancient Kingdom which was led by Lunarians and later with the Proto-World Government Organisation. Before to die Joyboy creates the Nika Nika Fruit using his old friend DNA awaiting Nika successor.
Roger at Lough Tale knew everything about Nika and Joyboy and orders to Shanks to find the New Nika through the world and find the Nika Nika Fruit and give it to Ace at the beginning, after the death of Rouge, the former Nika Nika Fruit user.
According to me :
Dark Dark Fruit is not in reality a Logia but a Mythological Zoan perfect evil counterpart of Nika Nika Fruit
Chopper's fruit is the Mythological Zoan Fruit : Hito Hito No Mi Model God Thot
Robin's fruit is in reality a Mythological Zoan fruit: Hito Hito No Mi Model Godness Morana-Kali)
Enel's fruit is reality a Mythological Zoan Fruit: Hito Hito No Mi Model Zeus/Raijin
For you?
