Crystal
The king of the flowers in the center (of England, if you remember) has a special crystal. The king crystal.
Picture the king holding this crystal aloft, giggling as the sun shines through it and sparkles.
えい
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The king thinks everyone wants his crystal so he hides it in the giant acorn (えい) in the center of the flowers in England. There's a tiny hole in the bottom of the acorn, and that's where this crystal stays hidden.
Imagine going to England, to the giant acorn in the center of the flowers, and searching for the king's crystal. If you find it, you can probably sell it for a fortune! Or just make a really sweet necklace.