On The Serpent's Tails
"About the place where it is located, do you have any idea about it?" Basil asked.
"We don't know for certain about it." Eloreth shook her head faintly. "We unfortunately can't send a lot of people to investigate it, lest we should cause a panic amongst the citizens."
The main reason why the Elves had decided to cover the real issue up was to not cause a panic. Weakened it might be, Yamata no Orochi was still a Mythical Beast that had terrorized the East for thousands of years before it was taken down.
Although many people had believed it was nothing more than a mere myth, now that the whole world believed such a thing did exist—especially the Elves who had always believed it—Yamata no Orochi's appearance would certainly shake the people.
Being the people of the Empire that hosted said Beast, pandemonium would definitely ensue in Padeitophys if they got to know it.
"You haven't said anything about the area where you encountered it," Basil remarked. "I am asking abut it."