Whether from Hoshido or Nohr, each member of the royal family had two retainers to both aid and assist them. And all are as different as the nobles they protect.
For Ryoma, his first retainer is Saizo, a ninja with near unparalled skill. He is the head of the Ignasto ninja trip and is the brother to Kaze.
Saizo's past is litered with pain, as him and Kaze's father was assassinated, and thus Saizo was given the burden of leading the tribe as well as being Ryoma's bodyguard. Then, when he tried to find his fathers killer, he was captured, tortured, and lost his eye before he could escape.
These things have hardened Saizo's personality, as he's often tempermental, and is perfectly fine not talking to anyone outside of Kaze.
That being said, he is eternally loyal to Ryoma, and can be to others if the supports are high enough. He is compassionate, helping others when he feels its honorable, but he doesn't deal with affection well, and often seeks to run away when such feelings are present.
Saizo is incredibly strong when leveled up, and can be a key member of your team if wanted.