Poor Ryoga. This boy is a very good-hearted soul, but has quite a few problems, which serve to make his life a living hell. First of all, he has absolutely NO sense of direction. He has to leave for his final destination at least a couple days before he expects to get there. In fact, in Junior High, Ryoga challanged Ranma to a duel because Ranma kept stealing the last bread of the day literally from Ryoga's mouth. The fight was scheduled to take place in an empty lot behind Ryoga's house. However, Ryoga somehow made a wrong turn and it took him four days to get there. Ranma waited for the first three days, but his dad took him to China on the fourth day. Ryoga followed them. All the way to Jusenkyo.
As he was looking over the cursed springs, a red-haired girl chasing a panda knocked him into Hietuenniichuan, Spring of Drowned Black Piglet. From now on, a splash of cold water turns him into a little black pig. When he emerged from the spring the panda grabbed him and gave the pig to a man to cook. The boiling water from the pot, changed Ryoga back into a boy. It was that he left to Japan to find Ranma, who he believed was indirectly responsible for Ryoga's new "problem." When Ryoga figures out Ranma was the red-haired girl, Ryoga is furious -- until he meets Akane. Akane immediatly saw Ryoga (as a black pig) and adopted him as her pet pig P-chan (P for pig, chan for cute). Upon seeing Akane, Ryoga instantly fell into love with her. Akane doesn't know Ryoga is really the pig she sleeps with at night and Ryoga plans to keep it that way. Could you imagine what Akane would think if she found out she was sleeping with Ryoga...
Ranma, being directly responsible for Ryoga's curse, is honorbound to tell nobody about Ryoga's curse. Of course, he does taunt Ryoga by, occasionally, calling him P-chan.
Ryoga hates Ranma for cursing him with his piggy form. As a result, he takes anything Ranma does as offending and fights him to "correct" the problem. He becomes even more furious when it is something that involves Akane, such as the appearance of another of Ranma's fiancees.