Unlike previous Mainstream Pokemon Games, two people can actually play this game at the same time in what is commonly referred to as Co-Op Play. When two players are playing with the set of Nintendo Switch JoyCons, they will travel through the Kanto Region together. Each player can have a Pokemon Follow behind their trainer if so wish to have one, and both players will actually throw Poke Balls when in a Wild Pokemon Encounter. Furthermore, all Pokemon Battles with other trainers will turn into double battles with each player selecting the moves for the Pokemon they send into battle.
However, whomever is playing as the second player will not be able to interact with any character within the game. They will not be able to pick up any Items found in the overworld, nor will they be the ones to start a Wild Pokemon Encounter. And, on top of these other restrictions, only the first player will be able to Ride on a Rideable Pokemon.