Board Thread:Questions and Answers/@comment-1754938-20150922055002/@comment-26976025-20150922223633

Maybe Rukia just never met him. The soul society is massive and not every soul reaper gets to see the captain of other squads. Maybe at the time of writing the story he was still undeceive on how to incorporate Isshin into the story. I mean it took until grand fishers return for us to find out he was a shinigami. And much later in the story before he was announced official as a captain. Could be story plot or Kubo just didn't know how to finish the story of Isshin.