Grand Arena Shop becomes available at team level 50. You can access it by tapping Shop in the Grand Arena menu:
You can also select the Grand Arena Shop tab when you open any other Shop:
Here you can spend Grand Arena Coins to purchase hero equipment, recipe fragments, Rune Stones, and Soul Stones of Lian, Markus, Ishmael, and Rufus.
New goods appear every 24 hours at 9:00 PM your in-game time. You can also refresh the Shop using emeralds.