"Cooper Clan Cosplayer" is an in-game achievement in Ghost of Tsushima that you can obtain by transforming the main character. This achievement is an Easter egg and reference to the character from the Sly Cooper action-adventure series - a striped raccoon in a blue suit with a yellow hook. It's important to adhere to these colors to unlock the achievement. Here's what you need to wear on Jin Sakai to look like Sly Cooper.

Gosaku's Armor

Gosaku's Armor can be obtained during the quest "The Unbreakable Gosaku". The quest is quite complex and extensive. First, you need to liberate 6 settlements, find a hill in the Old Togo Rice Fields, and battle a group of Mongols. The residents of the settlements you save will give you the key to the treasure chest where the mythical armor is hidden.

"Ocean's Guardian" Dye

The blue dye "Ocean's Guardian" is needed to change the color of Gosaku's armor. You can purchase the dye from merchants for 10 flowers.

Headband

The Headband can be found in the open world at the following location: Jogaku Temple, atop the pagoda. You'll recognize it by its characteristic blue color with a yellow hook in the center.

Mask

The "Thief's Wrap" Mask is randomly obtained along with gifts you receive as you progress through the game. It's likely to appear early on, so you won't have trouble finding it.

Katana and Tanto Skin

The set of swords "Sly Tanuki" visually resembles a raccoon's tail, so you'll recognize it immediately.

It's also found in the open world, lying atop a snowy peak in the Iwai Village area closer to the eastern side.

To obtain the achievement, simply equip all the specified items on the character. The achievement is awarded instantly.