Power He Knows Not

I Am Darkness Response: Harry starts to notice his magic reacting strangely whenever he was angry or scared; but then he hears about Sirius' apparent betrayal and he just snaps and so does his magic. What takes its place isn't a Saviour or a Destroyer; what takes its place is the true Power He Knows Not! Dark/Evil-Powerful Harry; Dark Harmony; OOC Characters;