To the People of Tsushima is a written record from the Records of Iki set, left by locals during the Mongol invasion. You find it at Drowned Man's Shore in Toyotama, and it counts toward the Avid Reader trophy.
Go to Drowned Man's Shore in Toyotama and look for the paper or scroll to read.
Image: Sucker Punch Productions / PlayStationBamboo Strikes
Bamboo Strikes are button-timing challenges where Jin slices a row of bamboo poles. There are 20 in all, 16 on Tsushima and 4 on Iki, and completing them raises your maximum Resolve.
Image: Sucker Punch Productions / PlayStationCharms
Charms are equippable trinkets that add perks to Jin, from extra health to silent arrows. You earn them from Shinto shrines, side tales and Legend ranks, and the six slots you can fill let you tune Jin for stealth, archery or swordplay.
Image: Sucker Punch Productions / PlayStationDyes
Dyes are colour variants for Jin's armor, bows and Sakai horse armor. Most come from merchants for flowers, others from tales, Wind Shrines, Sakai Banners or Baku in New Game+, and none change stats.
Image: Sucker Punch Productions / PlayStationHaiku
Haiku are short poems Jin writes at quiet, scenic spots on Tsushima and Iki Island. Each of the 19 open-world spots rewards a cosmetic headband, so this is where most of your headbands come from.