Hearthome City is a major location in Pokémon Brilliant Diamond & Shining Pearl, though you won’t be able to battle its Gym Leader just yet.
Your first time in Hearthome City will be pretty short in terms of main objectives to hit. Talk to the man on the first path into the city with the red hat, and he will lead you to the Contest Hall. There, you’ll find Fantina, the city’s Gym Leader - though she doesn’t want to battle you just yet.
Enter the Contest Hall to find Mom and Keira, and receive a dress or tuxedo - depending on which character appearance you chose at the start of the game.
After that, you should travel south, where you’ll meet up with your rival for a battle before leaving the city and moving on.
Your rival’s Pokémon, as always, depend on who you picked for your starter.
He will always start by having a Starly at the front of his team, so if you captured an Electric-type early in the game - like - you can one-hit K.O. this Pokémon pretty easily. There will be a Pokémon that’s weak to your starter (such as for ), and then of course, your rival’s starter.
Your rival is building a pretty diverse team by this point in the game, so it’s a good idea to have counters ready to go.
As with any city or town in the game, there are a few items to be picked up.
The first set is at the Poké Mart. Although more items get unlocked as you get more gym badges, you can expect a decent selection here the first time you arrive.
There are also many other items to be found around Hearthome city.
Mostly, the other locations are NPCs giving you tips on where to find things. There is also the Gym, where you will eventually battle Fantina, but you can’t do that right now - she’s the fifth Gym Leader, and you have a few badges to collect first.
Travel on to Route 209 to continue your journey.