Kuchiki Byakuya is, above all, a composed man.
When training, when working, when killing, he is impassive and precise. He find neither joy nor fear in battle, in same way another man would be unaffected by signing his name. It is for this very reason that he is such an efficient fighter.
But when a hollow catches him off guard, the injuries dealt by Kurosaki still healing, he is unable to resist as it invades his mind. His subordinates react too slowly, and can do nothing as their unconscious captain is abducted.
For days, Byakuya's memories are laid open. The hollow, a small dog-like creature built more for speed than strength, sifts through his mind like chaff. Occasionally it bites a limb, or rips out a chunk of flesh, to keep him weak from bloodloss. It searches out information about Soul Society, concentrating on things like patrol patterns and individual weaknesses. It also finds every failure, every blow to his pride.
On the third day, it finds the memories of the failed execution. It laughs and laughs, its voice slinking through Byakuya's head. Shinigami, it jeers, you are stupid, so terribly stupid. Everything you do is against yourself. I wonder what your little wife would say, if she knew how weak you really are?
And it crafts an image in his mind of Hisana looking at him in disgust.
Byakuya wakes up and puts his sword through its chest. His teeth are clenched as though to hold back his voice. The hollow laughs as it dies.
Drawn by his reiatsu spike, his subordinates arrive on the scene in time to see their captain, bloodied and disheveled, release his shikai on the corpse. When he finally solidifies it again, there is little left but a smear of blood on the ground.
They watch in horror as he crassly spits on the remains.