Although Ritsuka believed that his brother, Seimei to be a kind, gentle, and loving person, it was later revealed in the series that he had a violent personality, or destructive behavior at the very least. When Seimei reappeared in Septimal Moon, he attacked Ritsu and left him blind after having a short conversation about Soubi. Later that same evening, he wrote a haunting message saying “Ritsuka, I’m back,” on the wall using Ritsu’s blood.
Some suggestions have been made in the series that Seimei possesses greater powers than any normal sacrifice. Soubi is known to be almost afraid and spiteful of Seimei, and described his former “master” to be inhuman.