You Can Never Have Too Many...

When Genma was still training under Happosai, he got in a spot of trouble with a woman, Shiori Yamazaki. To get out of it, he made an agreement that if he should have a daughter, he would give her up to be raised by Shiori. Years later, Shiori finds that Genma seem to have hidden a daughter, Ranma, from her, and decides that having one of her sons marry Ranma will satisfy the agreement. So she sends her sons out to retrieve their potential bride.