Getting a Gigantamax Pikachu in Pokemon Sword & Shield involves having a Nintendo Switch with save data from Pokemon: Let's Go, Pikachu!. You don't have to reach a certain point in Let's Go, Pikachu! and it doesn't matter which profile has the save data. In Sword & Shield, speak to the NPCs in the back left corner of the Wild Area Train Station at the Meetup Spot. You'll receive a Pikachu with perfect individual values ​​​​(IVs) and the Gigantamax Factor that you can add to your party immediately.