Scabbard of Sharpening
This leather scabbard has been polished through long use and frequent care. When a sword is inserted into it for 12 or more hours it gives the blade an unnatural sharpness. The first 10 hits with this sword get a +1 bonus to attack and damage rolls. This effect fades once the sword is used 10 times or is unsheathed for more than 1 hour.
Dwarven smiths of old would make scabbards like these to give to their best human allies, granting them an advantage right at the start of combat. There are rumors that the dwarves reserved for themselves much rarer and more magical versions that had the same effect on a battle axe in its hanger. All without having to touch the axe’s blades.