Here is the story text for Chapter 10-
You have done it, Young Ruler! You have brought back the Fire Lilies and the Ice Lilies, and forged the legendary Mastery Sword. You have proven your knowledge of the proper, safe handling of mystical beasts, and fended off an attack from such creatures. In doing so, you successfully retrieved the fabled Hero's Crest. There is but one thing left to do... It is time, at last, to complete the ritual to reveal the Dragon Stone!
I haven't gotten a single Naga all day. They showed up pretty often before I reached the goal (Chapter 6). But since I placed and shopped the Naga trap, they never show up anymore.