PokillionaireHiroshima has a Bookoff that earned 5/5 stars. I'd visit the city just for this shop.
Bookoff Super Bazaar: Shockingly strong selection. Excellent prices. 20% off on some cards ON TOP of Tax Free.
Also: C-Labo Hiroshima (4/5), Sunrise Hiroshima (4/5), and LHUB (3.75/5) with a "Buy 10 AR Get 1 Free" promo.