Since the “Book” gives upgrades that are necessary to be competitive late-game, I think that it’s necessary to add 3 and 4 star chests to the market.
Since this would potentially unbalance the early game, I think that these chests should be added to the glory medal shop. That way, late-game players can complete the book without it affecting earlier gameplay.
As an alternative suggestion, a new “completion” shop which includes these chests, a small amount of each pet fragment, and so on would solve the book issue entirely. If considering this idea, I would suggest making a new currency that is only awarded to the top 3 ranks in SS tier to limit shop access to late-game players and to encourage players to move up in the arena.
Thank you.