Ash, Misty and Pikachu have made it to Pewter City. They briefly meet a rock
seller - named Flint - who lives on the outskirts of the city. Ash and Pikachu go to challenge the local gym leader, Brock. However (as you would imagine), Ash's Pikachu is no match for Brock's Onix. Defeated and disappointed, Ash and Pikachu leave the gym, and meet up with Flint again, who wants to help them.
Flint helps to power-up Pikachu. Then he shows why Brock has to be a gym leader and not go travelling on his own Pokémon journey; he has 10 younger brothers and sisters to take care of, after their mother died and their father left home. Ash goes to challenge Brock again. Pikachu beats Geodude (!), but is almost beaten by Onix... however, the sprinkler system goes off, and Onix is weakened. But persuaded by Brock's siblings, Ash does not use this to his advantage and leaves the gym badge-less.
Brock follows him and gives him the Boulderbadge for beating him in being kind
to Pokémon. Then he tells Ash his dream - to be a Pokémon breeder - and asks Ash to do well in place of him. Flint turns up and says that Brock should follow his dream himself. Flint is actually Brock's father, and will take care of the siblings.