Yharnam Helm is a straw hat that nods to Bloodborne and its hunters. You earn it by finishing the Blood-Stained Shrine, one of the Wind Shrines.
Find the Blood-Stained Shrine and clear it. The hat is the reward at the end, with a matching Kensei dye.
Wear it with Yharnam Vestments for the full hunter look.
Ashen Straw Hat
Ashen Straw Hat is a hat that unlocks when you upgrade Ronin Attire to level IV. It is added automatically, so there is nothing to find in the world.
Betrayer's Hat
Betrayer's Hat is a straw hat you get by finishing "Shadow of the Samurai" in Jin's Journey. It is a story reward, so you cannot buy it.
Bloodstained Betrayer's Hat
Bloodstained Betrayer's Hat is a New Game+ hat sold by Baku the Voiceless for 5 Ghost flowers. It is not available in a first playthrough.
Bone White Straw Hat
Bone White Straw Hat is a New Game+ hat sold by Baku the Voiceless for 5 Ghost flowers. It is not available in a first playthrough.