Play The Edo Campaign. To obtain the Golden Frill (Shintasu no Shinsen), you must fulfill a certain number of missions. First up, kill Yoshiaki Mogami. Then save your ally Hideie Ukita, who was gullible enough to be lured into a trap. Defeat all the enemy generals around him to successfully rescue him. Some of your friends will now ditch you and turn traitor. Rebuke them by destroying all of them (Hiroie Yoshikawa, Hidemoto Mouri, and Hideaki Kobayakawa). You will then get another mission to return to the inside of the castle and defeat all of the generals there. Once you do, Kotarou Fuuma will appear and attempt to sneak attack your base from a secret door that opens in the west. Defeat him before he can arrive at your camp. Next, defeat the one guard captain inside the east door of the castle to open a door and find a captured ally general, Ekei Ankokuji. With the prisoner freed, you will receive a mission to escort him back to your base camp. Destroy everything in your path so he does not get distracted and feel obligated to hack at anything nearby (especially all the enemy generals that will ambush the two of you). Once done, make sure you enter the main castle from the north side. Defeat the general in the way there and you will find a sealed door. At the dead end Ekei Ankokuji will suggest another path from the south side. Once this happens, a precious item report will flash on screen and the weapon appears on the bridge between the two sections of the castle. Go to the south side and cross over to the north part of the castle, finding the weapon along the way.