Angel Sanctuary Vol. 1 (manga)

Why is Setsuna so mixed up? Despite his attempts to be noble, he'll fight anyone anytime; he ignores all authority; and he harbors feelings for his sister that can only be described as "incestuous." Why is he such a mess? The reason may be found with two demons from the underworld and their enemy, an insane angel who is distributing an insidious computer game called Angel Santuary.