Ninja Shirt

Every part comes off King Slime, one at a time, and each kill gives you a single roll at one of the three. Duplicates are common, so a full outfit usually takes several fights. He turns up by himself during a slime rain, but waiting on the weather is slow. A handful of Slime Crowns lets you call him back to back until the gaps fill in, which turns the whole thing from a luck problem into a shopping problem.

On Expert and above he leaves a treasure bag instead, and that bag hands over two pieces at once. It roughly halves the number of times you have to fight him, so if you are on a higher difficulty and the drops seem to have stopped, check the bag rather than the floor.

This is armor for a fast, aggressive early character. The critical rate is spread across all three pieces and applies to whatever weapon you brought, rather than being locked to one class, and the movement bonus is large for this stage of a world. Defense is the price, and it is thin enough that you cannot stand still and trade hits in it. Wearing all three also leaves an afterimage trailing behind you, which is an easy visual check that the bonus is live. Anything with real armor value overtakes it once the dungeon or the Underworld opens up.

For years this was pure vanity with no stats at all, then it became a thrown weapon set, and the critical strike bonus it carries now is what replaced those throwing perks when that class was folded away. That history is why it looks like an outfit rather than something smelted out of ore. The design is close to the ninja job class from the early Final Fantasy games, color aside.