BUR #42890 is pending approval.
create implication hololive_(main_branch) -> hololive
create implication nijisanji_(main_branch) -> nijisanji
I think it's about time. If this has been discussed before then I couldn't find it.
Both agencies have multiple offshoot branches with their own tags but no way to search for just the original, and the branches speak different languages so it can't be uncommon to only care about one. Excluding the branch tags cuts out a lot of cross-branch group pictures you might want to see, and because of VirtuaReal you can't even exclude all of Nijisanji's foreign branches in a two-tag search.
If we do this then populating with a big mass update over all the related chartags would get near everything but the odd no_humans scenery type post, it would just be a pain to type up. They're sometimes called Nijisanji JP and Hololive Japan which as far as I can tell are both unofficial (and in Nijisanji's case, inaccurate) names but they might be useful aliases.