Knight Hunters: Weiß Kreuz (2001)

During the day, they're four cute boys who run their flower shop. By night, they instantly turn from innocent to bad as they go out and execute the people who do illegal things. Assassins. The group, Weiss (pronounced Vais) consists of the serious leader, Aya Fujimiya, the soccer lover, Ken Hidaka, the young computer expert, Omi Tsukiyono, and the playboy, Youji Kudou. Their boss, Persia, gives them their missions by tape recording, delivered to them by his secretary, Manx. As the story goes on, they find out the people they're killing have some connection to one of two other assassin groups, Schrient (pronounced SHRAI-ent) and Schwarz (pronouced Sh-VARTS). Along the way, the four's pasts are revealed and it seems that Aya and Omi have more issues with the Takatori family and the other two...