On the subject of relations, posts like post #464922 irk me a bit. It's obviously fanart of orenji_zerii's Touhou wrestling series, but I don't know how to mark it as such. The series doesn't have its own copyright tag, the characters are stock Touhou characters, there's no specific image to enchild it to, and it doesn't belong in the pool.
The best way I see would be to create a copyright tag, but that would add clutter, and it wouldn't be immediately obvious why the pool had a copyright tag when most other series don't.