That wasnt Kaien, that was the 9th Espada Aaroniero Arruruerie after there battle she was about to be finished off da the 7th Espada Zommari Leroux, Byakuya Kuchiki appears and kills him saving her in the process, she is later healed da Isane Kotetsu.
byakuya was so cool in that. when zomari wanted to finish rukia off he just appears staring at zomari. then he asks "are te the one who fought with THAT" gazes over and looks at rukia..lol