Kirigakure Saizou is one of the Sanada Jyuuyuushi and also a very good ninja. He has been devoted to Yukimura since his childhood, and will even turn against other members of the Sanada clan to protect his master. He has even been critically injured defending Yukimura in battle.
Despite his devotion to Yukimura, Saizo is often exasperated by his master's casual attitude and often worries about him. But he respects and fears Yukimura's abilities and ultimately will do anything he says, and his selfless devotion has also earned Yukimura's respect and caring.