Tag to pool: celestial_stones

The tag celestial_stones is about an event with a theme (a Pixiv project), not a copyright.

Correct me if I'm wrong, but I believe this is material for a pool instead. I'd compare it with other pools of specific projects, like "Pixiv Bottle Meme" and "Draw a Character at Various Ages".

Notably, given the specific theme, the pool Celestial Stones would be a sup-pool of pool #4191 ("Unexpected Personifications").

Pixiv projects worth tagging are a copyrighted tag. They are not subjective and they are not based on a template, they're not pool material.

I'd say don't start putting them all in pool #4191 because at some point it ceases being unexpected.