The sheath swings empty in the breeze and serves no purpose like a freshly neutered dog's scrot. It should have never been a part of the vest if it wasn't going to include the sword(s). They removed the sheath from Lightning's Guardian Corps. outfit for the very same reason: it would have just flapped around lamely because we have nothing that would "sheath" in it (and it was probably a nightmare to animate properly anyway) and having the Blaze Edge as an actual weapon meant they couldn't have the handle sticking out as part of the model either.