Giryou

The brother of Jie Mei, a highly skilled blacksmith.

[Spoiler] He eventually goes insane from being unable to prevent her sacrifice. Filled with anger, remorse and regret, he hammered his body into the shaft of the spear. His spirit is trapped in the darkness of the spear, unlike his sister, and can greatly influence the user of the spear with his fury. Still, he has pledged his loyalty to Ushio. [/Spoiler]

(Source: Wikipedia)