I think:
A. Luffy becomes someone worthy of becoming Joy Boy
B. Joy Boy is a spirit or deity whatever with unbelievable power, capable of changing the world. In some part of the world, people refer to him as Nika, The Sun God.
C. Joy Boy can connect to anyone he wills to, via the paths of Haki, or Devil Fruit, or both.
D. There are certain requirements to become Joy Boy / inherit his will and also power. Maybe its
- Willpower stuff, or
- Certain creativity, out-of-the-box approach in order to always become individually stronger (be it Haki or Devil Fruit), thus unlocking the spiritual connection / path to make Joy Boy aware of one's presence, or
- Having the purest heart which dreams of an utopia (proving it by struggling for one's entire life to bring joy / peace to everyone), or
- The combination of all points above, or
- Some other stuff
D. Apparently Luffy check all the boxes and makes Joy Boy/Nika aware of his struggle
E. Joy Boy is Luffy's Excalibur (just like
@Monkey D Theories' said in his theory), every Great Pirates have tried to access to be at his audience/presence through various Haki or Devil Fruit - mediated methods. But Luffy is the only one worthy to access his presence.
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F. Imo Luffy will not be possessed by Joy Boy, and win against Kaidou because of it. It will betray the narrative build-up by Oda where Luffy has to be the one surpassing his rival of PK candidate. Instead, i hope Luffy will converse with Joy Boy's spirit...but instead of Joy Boy freely lending his powers to Luffy, Luffy will conquer that power himself and even figure out an absurd and super powerful application, unprecedented even by Joy Boy himself, cementing the rubber boi's worth.
?
