Because most people probably don't get the reference: Yogiri's code name, "ΑΩ," is a reference to the Bible (Revelation 22:13, to be exact). It is a description of God, especially Jesus, signifying His omnipotence in particular. Seeing as they only looked at him from the angle of his power, it's very apt. (For a Japanese author to actually do that much research into Western culture, especially religion, is very refreshing, I must say.)