Imu will be Luffy's final opponent or test before getting to the One piece ..? I should hope that Oda could developp more lore around it.

Joyboy (that was a being born from the Adam tree) could eventually have lost control of himself (or died) in the past because his companions abandonned him. And, he became Imu, an altered version of himself that lost the fruit of Nika, the Nika Nika no mi. The First Joyboy was the guardian and protector of the DF, and was maybe tricked by a someone. After that event, the Nika Nika fruit escaped of his hands.

Imu is a remanent version, the incarnation of the Joyboy during the 1st world that awaits someone to kill him (or unreverse him), so that his spirit can go away nad R.I.P.

And, if we think of it as a cycle of birth/death/renewal/regenaration, the so called "Ancient technology" that Vegapunk was looking after during the Egghead Arc is an hidden secret of this World kept under Imu's protection.

Imu is the one being from the Void century that survived that period of freedom, world unity under the Ancient technology of the advanced "Ancient Kingdom".

His memories were erased too, but still he is looking to regain memory/control of it 800 years later after the collapse of that Society/kingdom. This is due to Joyboy's dream and the will of D. And Imu is indeed or in fact trying to kill the Joyboy (wich he was in the past...) in order to break that cycle of eternity. So, Imu is going to wait for an encounter of long lasting date with Luffy, no necessarly for a direct fight, but in order to guide him to the end of the world and to reveal him the truth and history of the world. Wouldn't that be cool ?? It could also end nicely One piece's cycle.

Plus, the will of D is related to Conqueror's blood and the will to control the will of D. Imu might be a spirit breaker, because this is how you would be able to beat a conqueror first, you would have to break his spirit. And, Imu is collecting after the broken souls and feeds himself with the will of the defeated.

-This is why Imu is compounded up to 99% of Haki (as we witnessed during the God Valley flashback ...)

• Imu might have been a conqueror too, even a rival of Joyboy who tricked him and never accepted his place in the eyes of Joyboy. He was jealous and tried to détrôné him. Like the Second of his crew maybe ??