There was an impenetrable brightness about Urahara Kisuke. Always, he was merrily stalking through the halls, captain's haori flowing lightly behind him. At his side was constant darkness, one that never really seemed to eclipse that brightness. That darkness came with a wavy dark blue shock of hair and a scowling expression, one that never seemed to be fully penetrated by the brightness that Urahara carried about him.
Mayuri was the shadow cast by Urahara's sun and the darkness that seemed to lurk in all the corners of the Soul Society. To many of the younger shinigami, he was what remained of the older generation, the ones that hadn't changed, the ones that still held to the hollow pits and the more brutal punishments. To Urahara's brightness, he was the dark.