As the wiki says, it's literally just Aris but with pink eyes instead of blue, the only image not tagged with Aris as well is post #6209026 which I assume is a mistake. I wasn't sure if this is considered a spoiler or not (the part that mentions the above is not marked as such in the wiki) but a bunch of posts with <key> are tagged as such.
afaik it is, which is why I'm not quite convinced.
I'm not caught up on jp story but if this is true, we can always make a (mutually exclusive to <key>, unless both are in the same image)<key> (robot) chartag for such depictions.
I don't know if it makes much sense for us to imply <key> to Aris if half of her pics are going to be of the robot keychain. It seems to me that this case is closer to identical twins than a skin/costume.
I don't feel that implication's useful. I highly doubt anyone searching for <key>_(blue_archive) is looking for the robot.
Moreover, it will mean just about every single properly tagged picture of aris_(maid)_(blue_archive) will also be tagged <key>_(blue_archive), which will make it literally impossible to search for pictures of Maid Aris and non-robot Key together. (Edit: This is already difficult to do because people have been tagging the proposed implication manually and inconsistently, so the tags need to be cleaned up, but I think one ought to be able to find images like post #6247694 via chartags.)
I think we should look to precedents like barbatos (genshin impact) and rex lapis (genshin impact) which aren't implicated to their humanoid forms, though those have the confounding factor of being bigger spoilers than Robot Key are.
I've updated the wikis. Unfortunately, I can't think of a good way to advise users on how to use the tag, without spoiling anyone who looks at the wikis while not already aware of Key's robot form. We could spoiler tag it like on the Genshin Impact characters' wiki pages, but I'm not sure it's a big enough deal to warrant that. This whole thing feels trivial with plana (blue archive) also being an unavoidable spoiler.