Kunitsu-Gami: Path of the Goddess

You have only a single slot for Tsuba Guards once you obtain the first by entering the Tent on a completed stage. In order to unlock the other two slots, you will need to wait until you have the ability to upgrade Soh just like you can the villagers, which is earned after beating the boss Seethe at Moegi Ridge (Stage 6).

You will now need 60 Musubi to buy both of the upgrades for slots 2 and 3. Earn Musubi by completing certain optional objectives, digging up black chests with the Thief and repairing certain objects in completed stages in the base mode. Once you have each slot unlocked, equip a guard to it and beat any boss or stage to pop the achievement. You can easily have 3 Tsuba Guards by the time you even reach Moegi Ridge if you are diligent at purging each stage of Defilement and collecting the rewards from the small shrines for doing so.