Ok. I'm confused at what are the intended boundaries of the Original tag, as mentioned in the current banner announcement. The banner mentions "corporate copyright". But what about well established characters from fan artists. Characters that have appeared in a lot of art. But there is no corporate copyright involved.
The thing that comes right to mind is Xierra099's Lovin Sis. These are currently tagged with the copyright tag of the webcomic series name. There is no corporate copyright involved, just Xierra099's copyright. Should every one of these pics be tagger Original? What about the Succubus girl I recently posted? Another Xierra creation, she has only appeared in one webcomic strip from Xierra as far as I know.
While Study Partners has no characters that are likely to fit the loli/shota/cub theme of the site it's another major fan-created series that raises similar questions.
Hazbin Hotel and Satina are similar properties that don't really have a corporate copyright.
As is normal for this kind of thing, there are lots and lots of examples on either side of the issue where it is 100% obvious what is the right decision. But it is the cases in the middle that are the tricky part, where the answers become blurry.