Many people have mentioned this before, although don't try to classify characters as good or evil. It has been mentioned that auras are probably inactive during unconciousness, therefore the aura of The Phantom Slasher inside a being may be incited by such a situation, that is, when the dominant aura is out of action. However, don't conclude that Rhue is the Phantom Slahser or indeed, any other characters. The Phantom Slasher could be an aura existant in all shadow swords, and weilders are capable of becoming it. We don't really know. I don't think Lun would make The Phantom Slasher as easily recognised just yet.
PS WONT KILL IN LIGHT? even in Episode 1, 2, and 3 u see PS following rhue in the DAYLIGHT? means hes active at DAYTIME.
A story told mainly from one man's view could display this at metaphoric. I don't believe we have ever seen him kill in light.