Just as Byakuya Kuchiki talks to his late wife Hisana's photograph, he writes to her... moments of peace and calm, which feels much the same to him as conversing with that beloved image at her shrine. - My interpretation of Byakuya's actions, thoughts which go by this enigmatic, outwardly calm, collected and aloof Shinigami's head, him with all his pride and even that arrogance... who is actually a big softie, bound by the rigors of his society, his responsibilities as the head of the Kuchiki clan and an elite Soul Reaper, who loves his wife immensely and cares a great deal for his sister.
10 parts