灰泉

Haizen is one of five ayakashi selected to infiltrate Karasumori as a part of Kaguro's advance guard, along with Sanan, Sekia, and Haroku. They are each given a human skin disguise so that their presence will go undetected by the kekkaishi. He has the ability to melt kekkai with a green substance from his mouth.

(Source: Kekkaishi Wikia)