"So the children settled down in this world, freeing themselves from the original world that had made their childhoods so utterly miserable and dark. In this dreamland, they could do anything they wanted; there were none of those things they detested. Every scrap of land was filled with endless fun, and they awaited the arrival of the next millennium...."
"Meanwhile, the Elf King residing in the castle began to speak, 'This world has boundaries, which begin to expand once the monsters are sealed away, and then contract again as the millennial deadline approaches.'
The God of Roar was greatly shaken inside!
Although this was a fairy-tale-like manuscript with many details only briefly mentioned and not elaborated upon, the ending still made the God of Roar immediately understand what kind of story this was.
The so-called assimilation and mediocre monsters were actually forced maturity as they grew up.