EVOV1 has a running thing of calling all their characters Yuki, and e621 has tags for each one, whether they're a Charizard (yukizard_(evov1)) or a Lovander (yukivander_(evov1)) or a snake (snuki_(evov1)). However, there's also "human Yuki", who currently doesn't have a tag; the only way to reliably find just that character is to start with yuki_(evov1) and then methodically subtract out every other Yuki tag until you're left with just human Yuki. Obviously this is error-prone, and I found two images not tagged yugia_(evov1) in the process of trying this out.
I feel like yuki_(evov1) should be removed from any image which has another *_(evov1) tag and used exclusively for human Yuki. (While you're doing that, you can also merge zebra_zuki_(evov1) into zuki_(evov1) unless there's some reason for them to exist separately which I don't know about.)