Rain Hat

Both pieces come off Raincoat Zombies, which only turn up while it is actually raining, so this set is gated behind weather rather than progression. Rain comes around often enough that you will meet them without trying, but the hat and the coat roll separately and neither is generous, so finishing the pair usually spans several storms. If you want it sooner, flatten a stretch of ground near your base and fight there through a rainy night instead of chasing spawns underground.

There is no leg piece, so this never forms a complete armor loadout on its own, and there is no set bonus at all. That last part is unusual: every other working armor in the game rewards you for wearing the whole thing, and this one gives you nothing extra for matching. By the time you can farm it reliably the defense is beside the point. Treat it as a costume. Both pieces go in the social slots over your real gear, and you keep the look without giving anything up.

Only one other functional set is this short. The wizard gear is also just a hat and a body piece with no legs to go with it.