I’ve had this idea about Rukia’s bankai kimono, we all know her bankai is incredibly unstable due to her complete lack of any mastery over it & in fact, requires a great deal of spirit energy control in order to maintain the perfect rate at which her body freezes & then thaws. It’s always been evident to me that her garbs are very cumbersome, on the battlefield she’d be unable to move at all not only due to the mass amounts of clothing but also due to the focus she must maintain to keep her bankai stable.
So, if the kimono is more detrimental than advantageous, whats the point of its manifestation with her bankai? Well it’s quite possible the kimono is made entirely out of frozen reishi, Rukia shows great difficulty in controlling the circulation of cold energy in her body to manipulate its temperature & seeing as her bankai achievement was extremely rushed i think it’s fair to assume the kimono itself is Sode no Shirayuki’s way of ensuring Rukia’s body can remain in a frozen state. Rather than controlling her reishi to achieve that delicate balance in temperature, her bankai freezes her reishi into something solid to wear as Rukia lacks both the control & the skill to wield her own bankai efficiently ( Due to the fact that it’s form is still very primitive & hasn’t been developed ideally ) .