Tried doing a search, turns out there are even more *_connection tags then I thought. I've cleaned the interlinks a while ago, but given the amount, I don't know if it's a good idea to add the missing ones too as it'll certainly make their pages unnecessarily longer, and some of the tags only have less then 10 posts so it'd be weird to link them on others' page. I'm thinking of a tag group like "Crossover connections" maybe?
Meanwhile, there're also certain specific tags we might want to discuss about.
Nationality connection should probably be aliased or implied to country connection.
I'm not sure about the use of series connection since most crossovers within a series aren't tagged anyway.
Accessory connection may or may not be aliased to outfit connection, and we need a distinction between the two, such as post #4628050, post #3891011, post #157877, post #3814493