I suck at Making Summaries....... oh well.....
Toshiro Hitsugaya has a sister. A twin to be exact. Katsuin, Toshiro's twin appears in a different section of the Rukon District as him, and they are the only thing they remember about their lives in the world of the living.
Katsuin graduates the Soul Academy and becomes a Soul Reaper just as Ichigo Kurosaki shows up in the Seireitei. All is hectic as she is assigned to Squad 10. Big mistake.
Byakuya meets Katsuin for the first time when she is still in the academy and he feels something for a certain new Soul Reaper that he hasn't felt for anyone since his wife, Hisana, died.
**extraction from story**
I was sitting in front of my brother's desk and he had a smile on his face. "I bet you haven't noticed, but I think Byakuya likes you, and I think you like him too. For one example, the time we went to the world of the Living and played around on the Beach? Well correction, They played around on the Beach? You Fainted at the thought of seeing Byakuya shirtless. And we both stayed in the. hut because it was too hot." I nodded blushing and he continued "He kept asking about where you were and while you were passed out, he snuck in and held you in his lap." My eyes widened at that and my whole face turned red.
I decided to retaliate "Uh-huh and the part where you kept sneeking glances at Shiraishi in her bikini. Don't think I didn't see That." His face turned red and I smiled slightly.