"Another Human Evil. But which Beast would she be? Based on the order in which the known Human Evils appeared, she should be the Fifth Beast, right? From the current situation, she probably isn't complete yet. Could this Beast have split into two as well?"
Humanity's natural enemies in the Moon World were the Human Evils. Of the seven Human Evils, four were currently known. Naturally, the next to appear would be the Fifth Beast. It was a perfectly reasonable deduction.
Naturally, Shen Fei had no idea that his deduction was seriously mistaken. Koyanskaya was not the Fifth Beast, but half of the Fourth Beast. In other words, she shared a single Human Evil with Fou. Fou represented comparison, while she represented amusement. But under the current circumstances, getting it wrong did not matter much. From Koyanskaya's earlier words, it was clear that she would not become Chaldea's enemy for the time being. In other words, she currently had no way of attaining her complete form.
"Thank you for your enthusiastic and detailed explanation. There's broadly no problem with it. So, who exactly do you think I am?" Koyanskaya wore a faint smile, as though Sherlock Holmes had not just exposed her true nature.
"The only being I can imagine that could make a god capable of instantly causing Earth Whitening retreat like that is one possibility: an entity with the supernatural ability to freely transfer between different worlds, an ability that not even the Alien Apostles possess; a disaster that even the Alien God must avoid clashing with. Archer-class Orion was summoned in Atlantis, and here in Olympus, the conditions for his summoning have already been fulfilled. Put all those factors together, and the answer follows naturally.
An independent disaster, and an existence sufficient to bring a Grand-rank Heroic