The Charm of Kagu-Tsuchi is a major Melee charm, named for the kami of fire, in Ghost of Tsushima. You deal bonus damage while at half health or less. You get it by honoring the Plum Blossom Shrine in Izuhara.
Climb to the Plum Blossom Shrine, at Shigenori's Peak in Komatsu Prefecture, and honor it at the top. You can reach it without the grappling hook.
It pairs well with the Unyielding charms, which cut damage taken in the same health range.
Aaruul
Aaruul is one of the 50 Mongol Artifacts, pieces of the invaders' culture and warfare you can study. It sits at a camp south of Izuhara Clearing in Izuhara, and finding 20 artifacts counts toward the Know Your Enemy trophy.
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.
Adak Tree
Adak Tree is one of the 50 Mongol Artifacts, pieces of the invaders' culture and warfare you can study. It sits at Yoichi's Crossroads in Izuhara, and finding 20 artifacts counts toward the Know Your Enemy trophy.
Adventurer's Fortune
Adventurer's Fortune is a dye for Traveler's Attire. It costs 10 flowers at the Izuhara merchants. Like every dye it only changes colours.