No, it looks like it could be either Kashima or Katori, but without any trace of anything other than their shared uniform, one can't really confirm it.
Okay, but should we be tagging it if one can't SEE from the image that it is Mutsu? That would be 'tagging what you know', not 'tagging what you see'.
But you CAN see Mutsu. You just need some outside help to be certain it's her and not anyone else.
"Tag what you see, not what you know" applies to things that are happening off-screen, or things like tagging "green hair" for a character in a greyscale image or "dragon girl" for an image where the character is in full-human form. If you can see a tail, but not the rest of the features to make sure it's a dragon girl and not a lizard girl, but do know which character it is and that they're a dragon girl, then you should tag "dragon girl".
There's a post a couple pages back in the comments section now about how someone had trouble recognizing a character was supposed to be Utsuho in the bath because she didn't have her wings or third eye and was drawn in a different style... but she's still meant to be Utsuho. If you go down the road of saying that it's not taggable unless everyone can clearly identify that character, it opens a whole can of worms.
But you CAN see Mutsu. You just need some outside help to be certain it's her and not anyone else.
"Tag what you see, not what you know" applies to things that are happening off-screen, or things like tagging "green hair" for a character in a greyscale image or "dragon girl" for an image where the character is in full-human form. If you can see a tail, but not the rest of the features to make sure it's a dragon girl and not a lizard girl, but do know which character it is and that they're a dragon girl, then you should tag "dragon girl".
There's a post a couple pages back in the comments section now about how someone had trouble recognizing a character was supposed to be Utsuho in the bath because she didn't have her wings or third eye and was drawn in a different style... but she's still meant to be Utsuho. If you go down the road of saying that it's not taggable unless everyone can clearly identify that character, it opens a whole can of worms.
This is debatable, and is actually being debated right now on the forum. The consensus is that even if a character is a dragon girl, their appearance on its own merit should be able to correlate the tag, should it be tagged with it. Likewise, you could extrapolate how to do character identities in the same manner.
one question though, if we don't know who this is why tag it kantai collection, since the tweet did mention FGO and really this could just as easily be shielder from that, she meets all the reqs of busty and short (offscreen) hair.
Because the outfit is from kantai collection, and even if it was cosplay, the post would be tagged with the copyright and character name of the cosplay, as is procedure with cosplay.
It's grey with pantyhose but does kind of lack the epaulettes rigging of the katori or any stuff of the katori class, why wasn't katori cosplay added since only Katori has pantyhose.
Note I'm not blasting you for this, just curious as to the objection to tagging until we get a scan/full upload. Hell the only reason I noticed this was my waifu sense going off, if I didn't have an insanely busy week I might have found this pic and ended up tagging it myself
I'm not fully cognizant of all the ship-girls, as I quit playing kancolle years ago, when Taihou first released. Katori in particular is the much less popular of the two sisters, so I didn't notice there was a wardrobe difference between the two.