In the demo, the player controls the female character in Diamond, and the male character in Pearl, named "Diamond" and "Pearl", respectively. The player begins in Jubilife City, and Barry will give them a tour, during which the player has no control. At the end, Barry will drop the player off at the entrance to Route 203.
Upon taking a step onto Route 203, a Scientist will approach the player and give them a Pokétch, though it contains only the digital watch app and no other apps.
Upon reaching the end of Route 203, the player meets with Professor Rowan, and may speak with him to cause him to instantly evolve the player's Roselia into Roserade, with Rowan commenting that several Pokémon are able to evolve in the Sinnoh region that were previously thought to be unable to evolve.
The cave at the end of the route (which leads to Oreburgh Gate in the final version of the game) is blocked by Lucas/Dawn. If the player speaks with them, Lucas/Dawn will tell the player that they look forward to seeing them in the full version of the game, and then the demo ends and the game resets back to the title screen.
If the player blacks out at any point, the demo ends prematurely, also resetting back to the title screen. The demo will end automatically once ten minutes have passed, after two minutes; the demo will auto-reset to the title screen.