I think that he is doing what he thinks is right by pretending to not care so much about her. Like I was trying to tell my little brother the other night (because he hates Byakuya's guts for being that way) that in almost every manga the eldest sibling is always presented with a challange and they have to pretend that they care nothing for thier little sibling, or else the enemy might make a connection and take her captive.... or something worse...

And it absolutely shocks me that everyone that loves Byakuya answered this question, but not a single one gave thier reason why.

I have two younger brothers and I've never thought I should behave with them as Byakuya does with Rukia. I know that as the older sister I must be a model for them and I should help and protect them as I can. I have also an older sister so I can understand also Rukia's position. I think I wouldn't like if my sister were like him...

@Morrighan178-
You may be an older sibling, but you do not have the dangers of being a member (especially captain) of the thirteen court guard squads!

Totally agree with Animeanimal.

Well...he did mature with age...Byakuya was just like Ichigo when he was younger...hot headed and easily worked up...hes more calm now..but he does show he cares for his sister in his own way...the two are sort of alike both in how they talk to others and how they perceive "art"

I'm supportive but to be honest, it's his sister, his chioce.

I think so

I'm not saying he's a horrible brother, or he doesn't care about Rukia it's just, everytime I see them together it seems like he isn't even paying attention to her. I know he's done things to keep her safe, but that just seems more like he's just trying to keep his promise to Hisana.
But Animeanimal makes a good point. Maybe being distant is just his way of keeping her safe.

I think maybe he is a little bit too cool and distant. It probably is part of Kuchiki family thing, where the family can never be conceived to doing anything wrong, so Byukuya is afraid that she might do something to embarrass the Kuchihi clan. I think it also is part of the 'not wanting the rest of the Gotei 13 to think that he is doing her special favours thing' like when she joined Squad 13 she didn't become a seated officer (through her own volition), but I think Byukuya is somewhat afraid of this too.

he should get closer to her .they are are step-brothers.

He's too cool and distant but at the same time he's to over protective and dosent try to really get to know her and see how much she truly has grown that is the job of an older brother but in some aspects he takes it to the extreme

He is doing the right thing he promised his wife to protect Rukia

Over-protectiveness is sometimes good. But from another perspective, it makes the one who's protected feel like a burden and an annoyance. What if you're in Rukia's shoes, Byakuya?

He should pay more attention to her... Rukia deserved more care and concern from her highly respected Nii-sama.