In the Crown Tundra, there are two Main NPC Characters. These two people are Peony and Peonia, a father and daughter, and you will meet the two of them directly after arriving to Crown Tundra. The two will be arguing about how to spend there time in the Crown Tundra, and Peonia (commonly referred to as Nia) will ask for you to step in on her behalf. After doing so, Peony will challenge you to a battle. After the battle ends, Peony will see that Peonia has run off to participate in a Dynamax Adventure.
After going through your first Dynamax Adventure in the Max Lair, Peonia will come up with the idea for you to spend time with her dad doing what he wants while she stays back in the Max Liar and continues playing in Dynamax Adventures. After telling Peony the plan, the two of you will head to the town of Freezington and will begin completing Peony's Adventures. From there, you won't see Peonia again until after completing all three of Peony's Adventures and finishing the Crown Tundra Main Story.
After doing so, Peonia and Peony will be permanently found in the Max Liar. Peonia will give you some items and advice should you talk her at certain points. Outside of that, Peonia isn't of much use except for giving you specific paths for certain Legendary Pokemon in Dynamax Adventures (for the fee of five Dynite Ore).