The Ariake Bamboo Strike is a sword-timing challenge at Houren's Pasture in Izuhara. Cut through all the bamboo with the right buttons and it counts toward raising your maximum Resolve.
Stage one uses the first three poles: L1, Cross, Cross. Stage two adds two more: Cross, Cross. Stage three adds the last two: L1, Square.
Also at Houren's Pasture: a Sashimono Banner.
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.