Soul Shop becomes available once you evolve at least one of your heroes to the Absolute star. You can access the store by clicking Merchant on the main game screen:
Here you can spend Soul Coins to purchase hero equipment, Huge EXP Potions, and Jet's Soul Stones. New goods appear every 24 hours at 9:00 PM your local time zone. Also, you can refresh the shop using emeralds.
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 100 Soul Coins for one Soul Stone. Once you open the shop, you will be offered to trade the excessive Soul Stones.