Before I begin, I just want to credit @egin_kogan for his excellent contributions to the Dragon Ball tag for the past while for inspiring the topic, especially in cornering the Dragon Ball Online/Dragon Ball Xenoverse/Dragon Ball Heroes fanart that hasn't seen as much representation on Danbooru yet. But in the process, his copyright tagging highlights an issue that we should figure out a solution to, as difficult as it might be.
Now, a bit of context - Dragon Ball Online was a game that introduced a bunch of new side-material lore stuff, including characters (whether properly introduced or in concept form), and then when that game got shitcanned, this stuff got repurposed for Dragon Ball Xenoverse and Dragon Ball Heroes at basically around the same time, and then the material from Xenoverse was also reused in Heroes as well. So, for instance, Towa appeared in Online originally, and then reappeared in Xenoverse and Heroes, while Chronoa appeared first in Xenoverse, before reappearing in Heroes.
The question then becomes, when either of them have their normal basic designs, and there is no context for what game is being referenced (not even in tags used at the source), what are their copyrights? In some instances, egin's solution has been "all of the above", as seen in examples such as post #7787869 for Towa and post #7908791 for Chronoa. But that doesn't seem appropriate. Given their reappearances beyond their original contexts, we can't just tag them with the copyright they debuted with (it's why we don't tag Vegeta with Dragon Ball Z ad nauseam, only if the image references stuff related to Z too, as appearance-wise he's basically identical in Super). But we can't just tag them with Dragon Ball alone, because they aren't part of the core franchise, they are in their own corner of it.
So the solution seems to be that we should make a parent tag for Online, Xenoverse and Heroes in the end, right? But what would we even call that? To my understanding, the franchise nor the fanbase have a common term lumping them together, aided by the fact that while they have shared elements, all of them use them in their own ways, like parallel universes. Something like dragon_ball_games
would be too broad, catching stuff like FighterZ in it, while also tossing out stuff such as the manga and anime adaptations Heroes has received. Using the common terminology Heroes developed for the unique versions of existing characters these games have, Xeno (after Xenoverse), but dragon_ball_xeno
feels too ambiguous next to Xenoverse's tag.
I'm out of ideas personally, so I'm tossing it out to the public here to get more heads involved.