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I disagree. Rukia's perspective was more than just showing the changes in the mask, but the changes with Ichigo himself--as she noted first by looking into his eyes. She's been aware of his inner hollow as most likely by doing research from asking Byakuya/Urahara and the qualms he's faced with it. This chapter she notes the changes in the mask and connects it with Ichigo's troubles. Kubo bypasses what we normally would have expected of her to be afraid of the mask and goes directly to her concern for Ichigo himself. With her perspective we get a more in-depth realization of not only the fluctuating power that comes with the changing mask, but how it has been effecting him emotionally on a negative level. Rukia sees past the mask and focuses on the man behind it. She's the outlet to the readers for showing how it has changed Ichigo throughout his tribulations in Hueco Mundo and effected his personality.
Rukia noted changes in Ichigo before she noticed the mask. So, she already knew something was wrong with him and looked for a reason, which she got a clue with the mask. She already knows he has problems with his hollow, so it's not a stretch for her to associate what she noticed with his mask. Associating those things to me isn't some huge sign of amazingness only she can accomplish, but rather a clear observation other characters could also make. Also, Ichigo's own contradicting lines and failure to produce a mask show clearly how Ichigo has changed.
Now I'm confused on if you think Rukia has ever actually seen the mask or not. You are saying it is a big deal she isn't afraid of the mask, which implies this is the first time she has seen it. But previously you said it was important that she could tell between the different variations of the mask itself. So which is it? If she has seen it already, why should she be suddenly afraid? Even if she hasn't seen it, she says she knows it exists and has heard it changes. Still doesn't give reason for her to fear it.
But, I kinda think you are trying to relate this to Orihime XD If you are trying to relate this to Orihime fearing the mask, then yes, Orihime did fear it and Rukia has not. Orihime feared it, but then again, Orihime felt Ichigo's hollow reiatsu trying to take control of Ichigo. She witnessed the problem first hand, Rukia was told of the problem and knew what to expect.
At the least you must accept that UlquiHime is canonz
