Unlock new officers by doing the following:

Magoichi ...Clear any campaign
Masamune ... Clear any two campaigns
Shingen ... Clear Sanada's campaign
Kunoichi ... Clear Hanzo Hattori's and Shingen's stories
Keichi Maeda ... Clear Kenshin Uesugi's story
Okuni ... Clear Keiji Maeda's story
Goemon ... Clear Okuni's story
Ranmaru Mori ... Clear Mitsuhide Akechi's story
Noh ... Clear Ranmaru Mori's story
Nobunaga Oda ... Clear Oichi's, Magoichi's, and Noh's stories