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

The goddess Rista summons a hero to the rescue to save her world, which resembles a super-difficult game. This hero, Seiya Ryûgûin, is overpowered but has a problem: he is ten times too cautious! He's the type to buy three suits of armor: one to wear, one spare, and one spare for the spare. Not only does he collect a ridiculous quantity of items, but he also spends his life in his room doing muscle training until he reaches the maximum level. When he does leave, it's to fight slimes at full power, just to avoid any risk.