Pika is a form of currency that is only seen in the games . Pika is the main form of currency in those games as opposed to Poké from most of the canon games.
Hey You, Pikachu!
Pika in this game can be earned mainly by completing certain events in the game. During events such as exploring on Springleaf Fields, the player can pick up items and after the day is over, they'll be able to earn Pika from the certain types of items they earn at the end. The items can be stored in the upper part of the toolbox in order to get the items. The player can also earn Pika by cooking a good dish during "A Pokémon Picnic" in Ochre Woods (with the Weird Dish being priced the lowest). Pika cannot be earned during events of Pikachu's Discovery Days.
Pika can be spent in Abra's Shop which can only be found in Springleaf Fields during Pikachu's Play Days or in Orche Woods during Pikachu's Daring Days. The Pika can be used to by various of items (the player must also watch out whenever Pikachu picks up edible items as it will eat it costing the player Pika).
Pika returns in this game with a far more valuable use and much more ways to earn it. Although now that the player cannot earn Pika by selling common items in this game, the player can earn Pika by selling their art to Professor Oak. This can be simply done by using the painting tool and submit the art to Smeargle who will display the art on it's art study show. Then, the player must then submit another art and by turning to the Report Channel or starting a different game, Oak will tell the player he has sold his/her art for a certain amount of Pika. The amount of work done on the art will depend on the number of Pika earned usually ranging from 50 Pika to 500 Pika. Pika can also be earned from local Pokémon after the player and Pikachu have already aquired their Nice Cards. They will always give out 10 Pika.
Another way to earn Pika is by competing in the two quiz shows in the game: Quiz Wobbuffet or Odd One Out. The faster the player answers the question, the more Pika he/she will earn. The Pika can then be spent on Shop N' Squirtle which can be used to by all sorts of items such as dolls, Nice Cards, and even Poké Minis. One of the most important items to buy are bus tickets to Viridan Forest, Mt. Snowfall, and Cobalt Coast which the two former are required to visit in order to complete the main game.