Depending on how high or low you rank you can get your sword customized at the swordsmith village. Like say Tsuchi or Hino plus get a few different options for customization. While Pillars are able to completely customize the sword they have. (Cosmetics only) - It just dont make sense for a mizu to have a custom sword at the start of the game except for their custom color. (re-post)
#Just a smol suggestion
west pier
Dont know how reasonable this is because im not a dev and I dont get how hard it is to make a game, so i dont know if this would be hard or easy to impliment. For designs for cosmetics I think that would take a while. :/
nimble saddle
I like this idea, a custom tsuba after reaching a high rank would be awesome and add to the whole rpg-thing, by personalizing things more.