Shinchou Yuusha: Kono Yuusha ga Ore Tueee Kuse ni Shinchou Sugiru

Goddess Listarte, the savior of the super hard-mode world Gairbrunde, summons a hero to her aid. The hero, Seiya Ryuuguuin, holds the cheat-rank status, but he is ridiculously cautious. For instance, he would buy three sets of armor: one to wear, a spare, and a spare for the spare. Beyond keeping an absurd amount of item stock, he remains in his room for muscle training till he reaches the max level and fights slimes at full power just to stay on the safe side.