There are 22 materials to collect for this trophy. You can get them by killing different Yokai or disassembling high grade equipment (you can see the material yo will get before disassembling).
You will get them naturally while playing and doing submissions, but there are specific ways to get them and this is what I'm going to explain in this guide.
First of all; to see how many of this materials you have, go to the items menu -> Smithing materials and sort by Rarity (pressing R3) and there will appear in the order of the list below.
The list of materials is this: (the first one is green, all the others are purple)
This first ones before the Yokai drop will be easy to get doing submissions, Twilight Missions and getting the Kodama Blessing in the shrine, so there will be no need to disassemble
Divine Fragment. You can get this material by disassembling a divine weapon
in the blacksmith menu when entering the starting point.
Highest Quality Tamahagane. To get this material just disassemble Katanas, Double Katana or Kusarigama.
Highest Quality Wood. To get this material just disassemble Spears, Bows or Rifles.
Highest Quality Ingot. To get this material just disassemble Axes, Canons or Feet protection.
Highest Quality Laquer. To get this material just disassemble Head protection (Light, Medium or Heavy).
Highest Quality Leather Cord. To get this material just disassemble Arm protection (Light, Medium or Heavy).
Highest Quality Leather Kozane. To get this material just disassemble
Light Chest, Legs and feet protection.
Highest Quality Iron Kozane. To get this material just disassemble
Heavy or Medium Chest, Legs and feet protection.
Demon's Horn. This is an easy drop from every Yokai you can find in any region.
Hank of Yokai Hair. Reward from Twilight Missions.
Kappa Shell. Kappa drop. In Kyushu Region, the sub mission "Finders, Keepers" is about hunting a Kappa. You can farm the material there.
Writhing Tongue. Onyudo drop. These are the Yokai with a large tongue, easy to find in almost every mission.
Bangasa Rib. Hino-enma drop. You can find her in the main mission “Deep in the Shadows” in Kyushu Region or Twilight Mission “An Ominous Cavern”. She can also be found as a mini-boss in three other missions: “The Silent Crow” sub mission in Sekigahara Region or “The Demon King Revealed” main mission in Omi Region.
Raven Tengu Feather. Raven Tengu drop. These are the Yokai that look like ravens with a sort of human body, easy to find in almost every mission.
Nue’s Claw. Nue drop. You can find this Yokai as a boss in the main mission “The Spirit Stone Slumbers” in Kyushu Region, this is the easiest way to get the drop, when you have the Eastern Side Key, open the door, and connect whit the temple, the fight boss is turning around in the first big door there. If you kill the monster and he drops the material just use a Hirimogi Branch to exit the mission. If you don’t get the drop, exit game, and continue, the load will be just before the fight. Just try until you get the Claw. He can also be found as a mini-boss in “The Demon King Revealed” main mission in Omi Region.
Great Centipede Fang. Great Centipede boss drop. You can find this Yokai as a boss in the main mission “The Silver Mine Writhes” in Chugoku Region. If you kill the monster and he drops the material the mission will end so you just must repeat it until he drops the material. This is an easy early mission, so with a high level there should be no problem. I got this at my second try.
Spider’s Leg Husk. Joro-gumo boss drop. You can find this boss in the main mission “Spider Nest Castle” in Kinki Region. If you kill the monster and he drops the material the mission will end so you just must repeat it until he drops the material. She can also be found as a mini-boss in “The Demon King Revealed” main mission in Omi Region. I got this material at my first playthrough, she must drop it easily.
Umi-bozu’s Eyestone. Umi-bozu boss drop. You can find this boss in the main mission “The Ocean Roars Agian” in Chugoku Region. If you kill the monster and he drops the material the mission will end so you just must repeat it until he drops the material.
White Tiger Fur. White Tiger boss drop. You can find this Yokai as a boss in the main mission “The Spirit Stone Slumbers” in Kyushu Region, the same mission where you can farm Nue’s Claw. If you kill the monster and he drops the material the mission will end so you just must repeat it until he drops the material. He can also be found in Twilight mission “The Best and the Worst”.
Ogress Claw. Ogress boss drop. You can find this boss in the main mission “Memories od Death-Lilies” in Tokai Region. She can also be found in Twilight mission “The Bleeding Spider Lilly”.
Gargantuan Tail Bone. Gasha Dokuro boss drop. You can find this boss in the main mission “The Source of Evil” in Sekigahara Region. This is the only way to get the material, if you don’t get it at first try, just restart the mission and as soon you can get in to the pit start the fight, there is no need to interact with the rocks.
Orochi Scale. You can get this material by killing Yamata-no-Orochi two times (repeat mission) in the main mission, The Demon King in Omi Region.