The Unaware Atelier Master

One day, Kurt, a kind-hearted boy, is suddenly kicked out of the Hero's Party for being "useless." He finds that his aptitude for weapons, magic, and all other combat-related skills is the lowest rand, so he takes odd-jobs repairing the castle walls and digging for minerals, where his exceptional abilities are immediately revealed. He proves to be skillful in cooking, building, mining, crafting magical tools—in fact, his aptitude for every skill unrelated to combat had an SSS-ranking! Kurt, however, seems completely unaware to his talent and ends up saving people, the town, and even the country through his unaware actions!?

(Source: AlphaPolis)