Because it was floating in the air and probably well guarded. The reason why they all shattered could probably be attributed to physics (yes, it still exists).
As for why Secret's not allowed to know, hindsight says that one or more of them might be tied to cleansing tainted shards or that...
And yet she lived longer than all those other villagers who were right-handed. It's clear that Secret laughs in the face of statistics and uses her Dodge Charms to avoid science.
Well, Tsukiko means "moon child" in Japanese, and it's a common enough name that it gets picked up by us 外国人
Also, I tend to be horrible with creating names, so you get a pass from me, anyway.