I don't think the forgotten gods are larping as little girls, since the reason they're the forgotten gods is because they forgot their own name and role. Everyone on earth has long since forgotten them, they stopped existing as gods. But it's because they forgot everything that they could become a new person, a new role. Which is what sensei meant in volume F by "she's real", even if you were someone once before a long time ago, your new self is also real and shouldn't be denied. There's no falsehood with them. Which is also why I don't think there was any sort of war or conquest with the forgotten gods or the nameless gods, after all the forgotten gods had already long since lost their names. They were effectively reset into new people, this is like their fresh start at a new life. They basically imply Shiroko just came into existence in this world, there's no saying it didn't happen to the others.