To Lord Sakai Upon Your Return is a written record from the Records of Iki set, left by locals during the Mongol invasion. You find it at Fort Sakai on Iki Island, and it counts toward the Avid Reader trophy.
Go to Fort Sakai on Iki Island and look for the paper or scroll to read. Fort Sakai is a Mongol-held territory, so expect to fight or sneak past guards before you can search it.
Also at Fort Sakai: the record To My Wife and a Sakai Banner.
To My Wife
To My Wife is a written record from the Records of Iki set, left by locals during the Mongol invasion. You find it at Fort Sakai on Iki Island, and it counts toward the Avid Reader trophy.
A Scrawled Message
A Scrawled Message is a written record from the Records of Iki set, left by locals during the Mongol invasion. You find it at a camp south of Lake Nagata on Iki Island, and it counts toward the Avid Reader trophy.
Attached to an Old Crate
Attached to an Old Crate is a written record from the Records of Iki set, left by locals during the Mongol invasion. You find it at a shed northwest of Lone Spirit Fall on Iki Island, and it counts toward the Avid Reader trophy.
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.