(All credits to Ricky for thinking this up) The balance between light and dark is crucial... "More Sake!"
Yang Kaido is a man of many faces and a complex nature. He prefers for his true emotions never to be seen and hides under the guise of a jokester. He is a deep and serious thinker, a poet of sorts, and a defender of Gotei 13. In most situations he is happy to keep a light heart and joke around unless duty calls in which case the smiles fade and his serious nature arises.
Shunido - A custom technique created by Yang a combination of Shunpo and Sonido Yang uses this technique to push his body into a flash making him one of the fastest beings Arrancar or Shinigami
Yang Kaido wasn't much of a human as humans go. He was dull and most people didn't pay attention to him. His only redeeming factor was that he was a slight oddball, always claiming to see spirits and outlines of monsters. Most villagers just shook this off. One day while helping a spirit Yang came across one of these monsters and in an attempt to defeat it to defend a spirit Yang was easily killed. He awoke to a white haired boy kneeling over him. One who would come to be known as Shoya his brother. He and Shoya quickly formed a 'family' to survive the cruel afterworld especially in the poorer sectors of the Rukon District. Shoya took on the name Kaido, even though he was 2 years (physically) older than Yang because he thought it sounded cooler. As Yang learned the basics about hollow he found himself exploring the Rukon district at every sighting of a hollow. Most often he avoided being seen but steadily trained to defeat them and become strong. When he believed himself strong enough to take one on he challenged a hollow and was easily thrashed. As the hollow went for the kill Yang was saved by a shinigami captain who recognized the boy's spiritual power and told him that if he wished for strength to join the Seireitei. It wasn't much of a decision for Yang. He told his brother immediately that he would be leaving. Shoya told him that it was a fool's errand but Yang was set in his heart. He departed for the Seireitei.
Yang seemed to naturally pick up all the talents needed to become a Shinigami. He was particularly good with Kido which led most to believe he would have a Kido based zanpakuto when he discovered its name. It was while training that he met a man named Domon Tsugetsa, the exact opposite of Yang. While Yang was serious and straightforward Domon was an obvious prankster, all the world his stage and every line his punchline. After a particularly destructive sparring match called by the teachers between the two clashing personalities they became friends. Yang graduated and found himself among the ranks of the Gotei 13 while Domon disappeared at some point in their Academy years. Yang quickly ascended in the ranks. He found himself serving under a particularly jealous and unscrupulous captain, but he figured the first chance he got he would simply change squads. He never got that chance...