The Charm of Dual Destruction II is a minor Melee charm in Ghost of Tsushima. Your attacks have a 10% chance to do double damage, twice the odds of the first version. You get it by finishing The Conspirator or A Final Request.
Any of these tales gives it as a reward: The Conspirator, A Final Request.
Seasons of War
Seasons of War is a dye for Samurai Clan Armor. It is a reward for completing "The Conspirator" (Masako's tales, part 8 of 9). Like every dye it only changes colours.
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.