Nagachika, Hideyoshi

Hideyoshi is a normal human and the best friend of Ken Kaneki. Hide is incredibly observant and can figure things out about people in a almost sherlock-like manner. He also becomes interested in things and works hard on them until he finds something else to interest him.

[Spoiler] In the Tokyo Ghoul manga, Hideyoshi goes missing, after his encounter with Kaneki.

Later in the manga, it is revealed that Hideyoshi has been helping several people such as Amon and Haise under the identity of Scarecrow. [/Spoiler]

(Source: Tokyo Ghoul Wikia)