So here's my theory

So stick with me, I've got a lot of thoughts.

We can at least confirm that Nunu used to be Mimi at some point due to the fact that he has to make a contract with people before he interferes with them, but he didn't have to with Mimi. And because he knew about the old women from Mimi's childhood in the slums.

I'm more than sure at this point that Nunu is the king from the original timeline in which Ebisu fell. Basically, my thought is that in his timeline, things went exactly as the MC described; there was a revolt against the king (possibly the same ones the MC just helped prevent), he was betrayed, and as a result, he was killed and encased in stone. This is how he later comes to meet the MC when he is revived as Rocky. However, once he dies as Rocky, his soul is finally cast into the land of the dead, where he somehow merges with some of the residual energy of Anubis and becomes a sort of demigod. And because the gods were long dead when the listeners tried to summon a god, Nunu was the one who was summoned rather than Horis, whom I think they were aiming for. He was the only god like presence left to summon, as the gods were long dead at that point, and because of his strong desire to save Ebisu, he also wanted to be summoned.

However, this still leaves us with a lot of questions.

1. Why did Nunu not recognise the MC initially, despite later saying he had previously seen him as a sort of ray of hope for Ebisu future?
2. How did Rocky have the seed to grow the necklace?
3. How did Rocky recognize the MC when he woke up?

To me, this could mean that, despite my initial theory, rather than Rocky being Nunu, he's actually Mimi. And that Nunu's timeline is an entirely separate one. So in that case, it could be that Nunu's time is the original timeline, but rather than turning into Rocky when he died, he goes straight to the land of the dead, where he becomes Anubis. And Mimi somehow ends up becoming Rocky and sending the MC to the past with his heart gem. However, it's implied that Rocky knew MC when he woke up, so maybe the Rocky Mimi was from a timeline where the MC had gone to the past before, but they failed to save Ebisu? And that the story we're currently reading is take three?