User blog comment:Wolf night10/The Final Getsuga Tenshou/@comment-2113144-20100611120705

Brother-bankai, I agree with what you said. Back when Ichigo faced off against Byakuya, when he was gathering all of that spiritual energy to unleash bankai, I recall Byakuya thinking to himself "How can he possess such reiatsu? It's almost as if he's..........." I'm thinking Ichigo and Isshin are part of one of the noble families, and if techniques are passed down, then that could explain it.