
[IT'S LOOONG!!] Personally, I don't like the theory about some time travel through El and his encounter with Alicorn. It's quite likely, but it complicates things terribly.
It seems that one of the theories is that El once lived, a long time ago, in the world where Alicorn was, as a human, but for some reason he died and reincarnated in our modern world, forgetting everything. But that's also a bit off, because Alicorn said El was using words he didn't know the meaning of. This means that El must already have had contact with words from the modern world. He came to this world by accident, then threw him back into ours?
OH! At first, the reincarnationists said that they had been looking for El's soul for a long time, because he was the next Water King. Then there must have been some kind of error in reincarnation a long time ago. They also said that his death in the modern world was not recorded as it should. This means that he never belonged there.
He was reincarnated in the modern world> Those who noticed their mistake in advance, tried to transfer him to the world with magic> There was an error (?), Maybe he died? > he returned to the modern world losing his memories and those from the world of the dead lost his soul data, they couldn't find him.
The fact that he looked the same (blue hair, eyes) meant that he reincarnated looking like the King of Water, but El himself didn't know it. Something went wrong? And I still don't know why El would be called "El". Therefore, your time travel theory is still more plausible. But why would he come back and forget it? Maybe someone accidentally sent him to the past to protect him? Therefore, El would look like the King of Water and even be one, but said he was human. To hide?
GRANDPA ERUHABEN LOOKING MIGHTY FINE ヾ(☆▽☆)