User blog comment:God of nothing/Shiba clan logic/@comment-1332195-20130501062344/@comment-4451464-20130503073206

well ukitake asked kaien to be a lieutenent 100-110 years before the show, and isshin was a captain nearly 80-90 years after that(20 years before the start) when kaien took the job, when isshin was promoted, and when kaien died are the 3 big questions, isshin didnt quit so much as he wanted to help a quincy and turned to a banished soulreaper for help(more then likely he was listed as MIA or deserting his post, which would lead to kaien alone being the sole pillar holding the clan in a high-standing, his death making them fall from grace)(isshin being the head of the "branch" family and kaien being the son of the head of the main family(isshin's brother maybe?), and the leader of the main family after isshin's abandonment of the soul society, and kaiens father's death)