Weiß: An Assassin and White Shaman

Weiss - an underground group of assassins composed of four men torn by their pasts; Omi Tsukiyono, Aya Fujimiya, Ken Hidaka and Youji Kudo. Each carrying the scars of their memories, they skillfully purge the city of criminals who have either evaded the law or are out of its reach. One by one, they begin to discover the relations of the crimes to something much more sinister, reaching out to their pasts. But each of them must decide if fighting for what they believe in and for the ones they love is worth it when it might come at the expense of their humanity... (summary from AnimeNewsNetwork)