Below is a list of all the costumes for Rab in Dragon Quest XI S. Rab is one of two characters that has a joke costume during a story event, which you can’t change out of during that event. This doesn’t stay after the story event is over, so you don’t have to worry about it.
The Sun Lord
The two pieces of equipment needed for this costume require you to find a recipe first, called Kit Fit for a King. You obtain this recipe by turning in 30 Mini Medals at the Mini Medal Academy. In order to forge the two items, you will need the following items: Gold Ore (x3), Platinum Ore, Red Eye, Silkblossom (x2), Magic Beast Hide, and a Green Eye.
The Grandest Master
This costume is exclusive to the Definitive Edition version of the game. Once you make it to the second part of the game, you will head to Mount Pang Lai. At the top of the mountain, there is a little shrine where you meet someone. There will be a chest right next to that person, which contains the Grand Master’s Garb, the item needed for the costume.
The Sun King
You will need a recipe for the two items required for this costume. The recipe, titled Corking Kit for Kings, is obtained by completing the third trial in the Wheel of Harma. In order to forge the equipment for the costume, you will need the following items: Slime Crown, Fire Ball (x2), Equable Emerald (x2), Colourful Cocoon, Technicolour Dreamcloth (x2), and Royal Ruby (x2).
The King of the World Tree
You will need to find the recipe for the two items required for this costume. The recipe, What a Wonderful World Tree, is found in a chest in The Sage’s Trial - The Fierce Forest. In order for forge the equipment to gain this costume, you will need the following items: Slime Crown, Royal Ruby (x2), Gold Nuglet (x2), Yggdrasil Leaf, Silkblossom (x3), Gold Bar, and Glimmergrass (x2).
The Sun God
Like most of Rab’s costumes, you will need a recipe for this one, since the two pieces of equipment are tied to it. The recipe, A Guide to Godly Getup, is obtained by completing the final trial in the Wheel of Harma (not the secret trial) in under 40 turns. In order to forge both pieces of equipment for this costume, you will need the following items: Slime Crown, Fire Ball (x2), Spectralite (x2), Technicolour Dreamcloth, Crimsonite, Kaleidocloth (x3), Uber Agate of Evolution, Serpent’s Skin (x2), and a Dieamend.