Yan

Yan was a Chinese Ghoul associated with the gang Chi She Lian.

Past
During his time in China, Kousuke Houji was involved in the destruction of the gang Chi She Lian. Among it's members was Yan, an associate of Tatara -- the Ghoul that would become Aogiri Tree's second-in-command.

Anteiku Raid
Upon realizing that he was facing Houji's subordinate, Tatara demanded to know whether Houji had Yan.

Tatara
Their exact relationship is unknown, though it is clear that Tatara bears a grudge against Houji as a result of Yan's presumed death.

Trivia

 * Yan is theorized to be the Ghoul used to create Chi She, the Quinque wielded by Houji against Yoshimura.