Hero of Tsushima is a golden mask from the Hero of Tsushima Armor bonus. If your edition includes it, it unlocks after the Prologue and changes only how Jin looks.
Own an edition with the Hero of Tsushima Armor bonus and finish the Prologue. The mask is added for you.
Adachi Dragon Mask
Adachi Dragon Mask is a New Game+ mask sold by Baku the Voiceless for 5 Ghost flowers. It does not exist in a first playthrough.
Adachi Half Mask
Adachi Half Mask is a mask you get by finishing "The Sister Betrayed", from Masako's tales, part 9 of 9. It is a story reward, so playing the tale is the only way to add it.
Ancient Dragon
Ancient Dragon is a New Game+ mask sold by Baku the Voiceless for 5 Ghost flowers. It does not exist in a first playthrough.
Avenging Lord
Avenging Lord is a mask waiting at a Gift Altar once you finish "The Broken Blacksmith" in Jin's Journey. Each main story milestone unlocks a different altar mask.