Ok hear me out, the legendary devil fruit that was kept safe in Elbaph for 800 years was the Nika devil fruit.

This is how the story goes:

Loki is interested in Lola and approaches Big Mom. This happens when Luffy is 6 and Lola should be 13.Though Lola is too young, I wouldn’t put past Big Mom and Loki to consider the alliance. Especially a giant alliance which could make her King of the Pirates.

Big Mom agrees to the marriage, but Lola rejects Loki and runs off. Loki is dejected and fights the king/his father Odin for the legendary devil fruit.

Loki is probably too strong, and he would get the devil fruit if they fight. The king knows this, so he swaps the original legendary fruit with another similar one and eats the legendary fruit to save it from Loki.

Loki kills the king and the devil fruit is reborn outside Elbaph for the first time. Loki eats the swapped devil fruit in front of everyone in Elbaph so everyone thinks he is sun god. Even the World Government.

Only Shanks knows about the king’s trick. When it’s respawned, he steals it from Who’s Who in East Blue and stays there for a year.

The giants are probably fighting Loki in Elbaph so can’t return back. Only this would explain why he didn’t do anything with the devil fruit for a year.

Luffy being Luffy, eats it when he is 7, and the saga begins.

The Nika devil fruit literally travelled to the other side of the world to get to Luffy. Shanks saves Luffy at the cost of his hand and leaves East Blue right after that, as he longer needs to stay.