Yotaro is seemingly a sickly child that refuses to get out of bed unless his mother can give him a pet panda. When Genma happens along, he is treated like a king by this rich family in exchange for being Yotaro's pet.
(Source: Ranma Wiki)

Years ago, Genma promised his old friend Soun Tendo that Ranma would marry one of Soun’s three daughters and carry on the family’s martial arts school. Except that the girl picked to be Ranma’s bride doesn’t seem to like him, Ranma keeps getting into fights…and did we mention that whole changing into a girl thing?
 
(Source: Viz Media)

Ranma Saotome, the boy who turns into a girl with a splash of water, always has his hands full fending off crazed admirers. One of the most fanatical is Shampoo, a girl from a tribe of Chinese Amazons who tried to kill girl Ranma, was defeated by boy Ranma, and then proposes marriage to him due to her clan's rule. Things get a little crazier when Shampoo falls into a cursed spring and turns into a cat! And even crazier when Mousse, who is in love with Shampoo, challenges Ranma to a battle over... Ranma's fiancee, Akane...? 
 
(Source: Viz Media) 
 
Note: Episodes 7-9 were originally meant to be seen between episodes 13 and 14 of the original series.

Yotarou