Hisagi Shuuhei is the son of Yae Kurosawa and Hisagi Mitsuhide. A former Captain in the Royal guard, he was exiled by Tsubaki.
Just to say, Shuuhei is Kensai, which is the highest level of Samurai ((imagine a Shinigami)). He was first in his order, joined the Guard at ten, and achieved rank of General by thirteen. He is by far the most skilled swordsman in the land.