In The Legend of Zelda: Breath of the Wild, Link donned a pretty iconic outfit. Ditching his trademark green in favor of a new blue look, Link's default style in BOTW was a stark difference, mirroring how different the game was from its predecessors.
Fast-forward to Tears of the Kingdom, and Link has yet another new look. Of course, if you're a fan of the old look, it is more than possible to sport it as a throwback. The blue Champion's Tunic is back under a different name, and while it's tricky to find, it's well worth the trouble for that dose of nostalgia.
Zelda's Secret Well
The first step on this quest is to find out where the Champion's Tunic actually resides - this involves going to Hateno Village and finding Zelda's Secret Well. You'll find this behind Link's old house - the one you can build in Breath of the Wild.
The well's coordinates are 3301, -2298, 0130.
Climb down the well and you'll find Zelda's diary and a treasure chest. Read Zelda's diary to begin this quest - it reveals that the Champion's Tunic is now beneath the castle throne room and notes that Torches are the key to it.
Open the chest to get the Well-Worn Hair Band, which will let you give Link the same hairdo he had in Breath of the Wild.
Acquiring The Champion's Tunic
As hinted at in Zelda's diary, the tunic is hidden in a secret area beneath the throne room in Hyrule Castle, which is floating above its usual location, surrounded by gloom.
An easy way to get there, as long as you have plenty of stamina (or stamina-restoring food) is to launch yourself up with the Lookout Landing Skyview Tower and fly right there. Having Tulin as a summon to Gust you closer will also help with this.
Once you've reached Hyrule Castle, enter the Sanctum. This is the throne room on 1F at the center of the building. Here, you'll find a throne with two braziers in front of it.
Use whatever means you want to light the two braziers (such as with Flint or with Fire Fruit), and you'll unlock a secret passage. Head down the newly-revealed hole to find a chest that contains the Champion's Leathers, which is this game's version of the Champion's Tunic.
The Champion's Leathers starts off with a defense value of five and can be upgraded by the Great Fairies.