The ending is that an immortal girl with a god complex created this world and considers everyone her toys. The protagonist learns the real historical names not because he has entered a parallel world, but because it is the same world that the creator has been resetting many times, and the protagonist is something like a residual effect that has accumulated and accumulated until it formed a personality, and that is why he vaguely remembers other incarnations of this world. And yes, of course, even Mu is not actually bad, but good, and the only bad character is the creator of the world.
Well, I didn't quite like that, but I did like the moment when we defeat her in the final fight, everyone is happy, they say their stereotypical phrases, and then the screen suddenly goes black with a shutdown sound, and an inscription appears, something like "Forced termination". And then this goddess appears, laughs, explains that she cannot be defeated and that she will now reset the world again. And then, of course, we defeat her with some kind of miracle.
Where do we end up when we save the world?