User blog comment:Xilinoc/Ch. 567 (Rukia be like "I ain't even scared though")/@comment-5147109-20140207231148/@comment-5147109-20140208144238

@Mohrpheus

It's about more than just reiatsu, if it was just pure reiatsu in play then they wouldn't even bother having different types of powers as it would simply be whoever has more reiatsu wins by default. Rukia's Zanpakuto can lower the temperature of anything around her, including the air, which would be exactly what needs to happen to counter Zanka No Tachi.