Seiji Midou

Kouhei's cousin and a powerful exorcist in his own right. Later in the series it is revealed that despite training his entire life, his powers are no match for Kouhei's latent potential. Because of this, he is slightly jealous of Kouhei. Seiji Mido (御堂 晴爾, same reading) is his writer's name.

(Source: Wikipedia, edited)