Ash [Satoshi], when he first started on his Pokemon journey, got a small Pokemon called Pikachu. Pikachu is an electric mouse, and didn't like Ash one bit, so needless to say the encounter was...shocking. Then, after a life-threatening experience, Ash and Pikachu. became best friends, and have continued that friendship for two and a half years.
Ash is slightly arrogant, and is generally very nice to people. Now, later in the series, he has developed his skills...and love interests. He seems to have tender feelings for a young girl named Misty [Kasumi] he befriended on his journey, and his feelings are made obvious when she has to leave him.
Misty and Ash first encountered each other under strange circumstances. Ash was trying to rush Pikachu to the Pokémon Center in Viridian City. In the process, he took off with Misty's bike. Misty would catch up with him and demand remittance for the bike... which got wrecked. Just to make sure Ash pays her back for the bike, she decides to go along with him (to Ash's dismay). Still, they become good friends during their adventures together, and the broken-bike really just becomes an excuse.
Misty is in actuality the youngest and least attractive (don't say that to her face) of four sisters. The three oldest (Daisy, Violet, and Lily) together are the leaders of the Cerulean City Pokémon gym, and Misty bitterly resents her relative tomboyishness. She is assertive to near-aggressiveness, and she doesn't mind bragging that she's a girl and better than the guys...when she isn't yelling at them after an insulting remark.
As you would expect, Misty's specialty is Water Pokémon, originally starting out with a Goldeen, a Staryu, and a Starmie. She will later acquire a Horsea, a Psyduck, a Corsola, and eventually a Poliwhirl.