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").
Updated by jjj14