There are two unique non-playable characters that can be unlocked only as bodyguards; Kojiro Sasaki and Katsuie Shibata. Both are unlocked by completing special missions in Survival Mode on 76F. If you have enough money, start from 51F and play until you reach 76F. You should use a powerful character with maxed stats such as Musashi, Tadakatsu or Keiji. Unlock Kojiro and Katsuie by performing the corresponding tasks:
Kojiro Sasaki Play the "Employment Opportunity" mission on 76F. On the first floor, score 100 KOs in five minutes. On the second floor, defeat Mitsunari Ishida, Yukimura Sanada and Kanetsugu Naoe in five minutes. On the third floor, defeat the same enemies in the second floor, but this time they are in Hyper mode and stronger than before. On the fourth floor, defeat Kojiro himself. He is in Hyper mode and has a few bodyguards. Avoid them and defeat Kojiro. On the fifth and final floor, defeat Musashi Miyamoto. He is in Super Hyper mode and is extremely strong, meaning that regular attacks will not stagger him. After defeating Musashi, you must defeat Kojiro again. He is in Super Hyper mode like Musashi. After defeating him, he will become available in the shop as a bodyguard.
Katsuie Play the "Woeful Beauty" mission on 76F. On the first floor, defeat Oichi. She has a few bodyguard officers. Avoid them and defeat her. On the second floor, you must approach Hideyoshi and defeat him in less than one minute. On the third floor, you must defeat Mitsuhide Akechi and Ranmaru Mori in three minutes. After defeating them, Nobunaga will appear and attempt to escape. You must defeat him immediately. On the fourth floor, you will face Nagamasa Azai's bodyguards, although it is not required to defeat them since they will constantly reappear again. Nagamasa will appear after a while. Avoid his bodyguards and defeat him to open the stairs. On the fifth and final floor, defeat Katsuie himself. He is in Super Hyper mode and is extremely strong, meaning that regular attacks will not stagger him. After defeating him, he will become available in the shop as a bodyguard.