The greatest Onmyouji in in the history of Japan, Abe no Seimei is the grandfather of Masahiro. He has Twelve shikigami under his command and is able to transfer his soul (which is in his younger form) outside of his old aged body, but this makes his body vulnerable. He teases Masahiro to push him further in his journey (which is kind of like a reverse psychology) and helps him out when he is in trouble. Masahiro calls Seimei "Old raccoon" when he is angry after Seimei's lecture/teasing of Masahiro's performance.

(Source: Wikipedia)