The Charm of Fortitude is a minor Defense charm in Ghost of Tsushima. A hit that would kill you has a 20% chance to leave you standing, and you gain Resolve when it does. You get it by finishing the tale The End of Suffering.
Complete The End of Suffering and the charm is part of its reward.
Clear Summer Headband
Clear Summer Headband is a headband you get from "The End of Suffering", a side tale (Norio's tales, part 7 of 9). There is nothing to search for: play the tale and it arrives with the rewards.
Akashima Bamboo Strike
The Akashima Bamboo Strike is a sword-timing challenge near Fort Ito in Toyotama. Cut through all the bamboo with the right buttons and it counts toward raising your maximum Resolve.
Akashima Haiku
The Akashima Haiku is a poem spot where the river meets the sea, just south of Old Kanazawa Marsh in Toyotama. Sit down, pick three lines and you earn the Headband of Uncertainty.
Akashima Lighthouse
Akashima Lighthouse is one of the 10 lighthouses Jin can relight, at Fort Ito, Toyotama. Lighting the fire gives a minor boost to your Legend.