The Soul Shop becomes available once you evolve at least one of your heroes to the Absolute Star (i.e., six stars) or receive Soul Coins for the first time. You can access the store by clicking Merchant on the main game screen:
Here you can spend Soul Coins to purchase Huge EXP Potions, hero equipment, and Jet's Soul Stones. New goods appear every 24 hours at 9:00 PM your in-game time zone. Also, you can refresh the shop using emeralds.
Note: The Soul Shop is the only place where you can get Jet.
You get Soul Coins by exchanging Soul Stones of absolute evolution heroes. The exchange rate is 1 Soul Stone = 100 Soul Coins. Once you open the shop, the game will offer you to trade the excessive Soul Stones.