Exactly like the Kayson Bookshop owner said, these eight books did mention Lantisde.
Taking away the three novels which should have just made up the name, the other five books all mentioned Lantisde.
Deducing from the trivial clues, Lantisde had once been a human kingdom on the Norland Continent, but it had always kept a low profile.
However, about 1000 years ago, everything about Lantisde disappeared as if it was erased from the Norland Continent in an instant. Everything, including all the records about it, disappeared mysteriously.
All the clues pointed in one direction: Lantisde was already lost, and nobody knew where it was.
Gina said she came from Lantisde, and the scenes she drew look like the bottom of the sea. Seems like Lantisde had sunk then, and was sealed at the bottom of the sea. However, they had also obtained the ability to live underwater from this…
This plot sounds rather familiar?