Astria Ascending

The final J-Ster challenges in the arena (again, Leo Temple) do not unlock until after the story, so don't bother until then. It's also much easier to win these once you have at least only Level 4-5 tokens in your inventory because of the random rule a few matches has. Again, once you get the hang of this game it becomes very easy. Few opponents carry a full deck of Level 5 tokens, so once you get a bunch of them, you should be able to win battles in one try.