Flowers are items in Casshern Sins that symbolize happiness, beauty and most of all, life.
Flowers appear frequently in the anime, Casshern Sins. They are normal flowers but they represent the life of whats left in a world where not nothing else seems to have a chance at survival. Luna, the life of the planet is known to fear death and because of that she is very fond of living flowers in bloom, due to their raidant sighns of life. Leda has mentioned how a baby represents a flower in bloom, simply a beautiful life. After Luna's rebirth, she felt that flowers could not represent life because they know death, as they eventually die. But Casshern and several others mention how one must know death in order to truely live, just like the flowers. Many episodes also mention flowers in their titles, reffering to life in the majority of the cases.
Luna once explained to Dune that flowers were the source of her happiness because when they're in Bloom, they can bring a smile to anyone's face. Even Dune who was a cold but ligh thearted robot believed in Flower's power to bring happiness to his love, Luna.
Niko, who watched over a beautiful flower garden believed that Flowers could make anything beautiful, they also seemed to keep her happy in her lonleyness. Ringo has also mentioned how flowers are one of the only beautiful things left on the planet, something still full of life, much like Casshern.