The last time the air spirit people showed up on easter island, the dungeon's security measures activated and the Aku Aku were released. Manu, along with the rest of his people, were all dragged into the cave of the cannibals. In the end, Manu was able to pass the trials and those who died during that period either became Aku Aku or were turned into moais.
Both cryptids, although enemies among them, had the same purpose. To keep the Air spirit from giving birth to a monstrosity. But that left some questions unanswered.
Nothing explained why Manu was able to live for so long, why did they air spirit people were so keen on breeding or why did the one who created the dungeon go as far as to put so many safety measures in place.
To answer those questions, Uriel went along a line of thought that was purely theoretical.