You need to unlock the required character and replay the mission in either free mode or story mode.

Unlockable	How to Unlock
Equippable Item: Bear Saddle	Achieve 1000 K.O.s and Clear Chapter 3: Battle of Yamazaki with either Zhang He in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Demon Mask	Achieve 1500 K.O.s and Clear Chapter 2: Battle of Nanzhong with Xiahou Ba in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Eight Hand Mirror	Achieve 2000 K.O.s and Clear Chapter 2: Battle of Hasedo with Kunoichi in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Elephant Saddle	Achieve 1500 K.O.s and Clear Chapter 3: Battle of Hulao Gate with Achilles in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Gauntlets of Malice	Achieve 1000 K.O.s and Clear Chapter 2: Battle of Xuchang with Sanzang in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Gauntlets of Vitality	Achieve 1500 K.O.s and Clear Chapter 2: Battle of Mt. Dingjun with No in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Gold Gauntlets	Achieve 1500 K.O.s and Clear Chapter 2: Battle of Kyushu with Sun Shangxiang in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Iron Armor	Achieve 1000 K.O.s and Clear Chapter 3: Battle of Tong Gate with Motonari Mori in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Iron Gauntlets	Achieve 1000 K.O.s and Clear Chapter 1: Battle of Nagashino with Zhou Tai in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Matsukaze Saddle	Achieve 1500 K.O.s and Clear Chapter 3: Battle of Honnoji with Ayane in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Musou Armor	Achieve 1500 K.O.s and Clear Chapter 1: Battle of Odawara Castle with Wang Yuanji in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Musou Magatama	Achieve 1500 K.O.s & Clear Chapter 1: Battle of Dongkou with Sun Wukong in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Pleiades Belt	Achieve 1000 K.O.s & Clear Chapter 3: Battle of Changban with Xiaoqiao or Ryu Hayabusa or Bao Sanniang in party. Complete on Hard or Chaos difficulty.
Equippable Item: Prayer Beads	Achieve 2000 K.O.s and Clear Chapter 1: Battle of Yiling with either Da Ji or Keiji Maeda in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Rabbitskin Leggings	Achieve 1000 K.O.s and Clear Chapter 3: Battle of Yangping Gate with either Nezha or Diaochan. Must complete on Hard or Chaos difficulty.
Equippable Item: Raiment of Unrest	Achieve 1000 K.O.s and Clear Chapter 1: Battle of Shouchun with Zhang Liao in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Red Hare Saddle	Achieve 1500 K.O.s & Clear Chapter 3: Battle of Fan Castle with either Xu Huang or Wang Yi or Joan of Arc in party. Complete on Hard/Chaos difficulty.
Equippable Item: Spirit Armor	Achieve 1500 K.O.s & Clear Chapter 1: Battle of Ueda Castle with Nobunaga Oda in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Sun Tzu's Art of War	Achieve 1500 K.O.s and Clear Chapter 3: Battle of Shi Zugatake with either Zhenji or Lu Bu or Ina in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Tome of Medicine	Achieve 1000 K.O.s and Clear Chapter 2: Battle of Sekigahara with Ranmaru Mori in party. Must complete on Hard or Chaos difficulty.
Equippable Item: True Vision	Achieve 1000 K.O.s and Clear Chapter 2: Battle of Luoyang with Dong Zhuo in party. Must complete on Hard or Chaos difficulty.
Equippable Item: Vestment of Voidance	Achieve 2000 K.O.s and Clear Chapter 2: Battle of Anegawa with either Huang Zhong or Guo Huai in party. Must complete on Hard or Chaos difficulty.