Confetto said:
I feel like there's a big difference between twins and counterpart characters that are meant to be slightly different situations.
Also, while there are variants that don't get implied (I'm reminded of Dark Link and Nega Scott, for example), it's generally more of a case-by-case thing, which I feel is probably best, standardizing how different character variants in wildly different franchises are handled seems like a recipe for disaster. I don't think I've ever seen someone say Nine isn't Tails, just that he's a different version of Tails. I usually see artists on other sites like Tumblr use both the main Tails tag and the more specific Nine tag.
The Shadow Mario argument is also misleading. No one's ever proposed an implication to begin with. This is the first time that tag has been mentioned in the forums. That's not to say an implication for him would be correct, but you can't really make claims about "why" it's not implied when no one's actually discussed whether it should be or not to begin with.
You distinguish twins from counterparts, but the key factor for tagging should be whether the source treats them as distinct individuals. Sinbad isn't Knuckles in the story, regardless of looks. Implying them merges distinct identities.
How artists tag on Tumblr isn't relevant. Danbooru needs precise search. If "nine_(sonic)" implies "tails_(sonic)", searching for "tails_(sonic) nine_(sonic)" fails to find images with both, which is a key use case implications break.
Let's say a user wants to find a picture of Amy Rose and Rusty Rose together.
"amy_rose rusty rose" does not work, because rusty implies amy.
Fair enough! This hypothetical user is very tag-savvy and know of the persona gentags. They know "amy_rose rusty rose dual persona" will do the trick.
However, they find post #6503706 and post #6548842 and post #9215129 instead, which depict Rusty alongside... Black Rose.
These images would show up for a search of "rusty_rose amy_rose dual_persona" as well as "black rose_(sonic_prime) amy_rose dual_persona" - there is no way to specify "I want to find a picture of Amy Rose and Rusty Rose together" if Rusty implies Amy.
If Amy is not implied, then a simple search like "amy_rose rusty_rose" is all I need to find this picture, which features Amy and Rusty:
(and Black Rose, showing a "dual persona" search would not work for finding Amy + Rusty here)
The biggest issue is that Sonic Prime's entire gimmick is that's it's based entirely around multiverse variants. It becomes objectively more difficult to find things if the variants are implied to the original character. Dedicated Sonic taggers haven't posted many Sonic Prime artworks, but the vast majority of them feature variants with other variants, or variants with the originals in the same image.
post #5930984 Nine with Rusty (No Tails or Amy)
post #5981372 Sonic with four variants, and none of the original cast. (Sonic with Dread, Nine, Rebel, and Thorn)
post #7865380 Tails with three of his variants. (Tails with Mangey, Nine, and Sails)
It wasn't as big of an issue when the Storybook games originally came out, as there was no interaction between the originals and their storybook counterparts, but when the entire show is based around variants interacting with each other, implies makes searches less accurate and less helpful.
Also, should we not be tagging images featuring the variants that made their debut in Sonic Prime "sonic prime" by default? They've all been featured prominently in Sonic Dash, Forces Speed Battle, Speed Simulator, etc, and no longer need it if we're going by the precedent set by those games. They're going to be in Sonic Racing: CrossWorlds, too. We're being inconsistent on whether to apply copytags outside of "sonic (series)" for subsequent appearances. Same goes for the Storybook characters as well, as they've been in both Dash and SFSB.