Nanao Yozakura is the fourth son and youngest sibling of the tenth generation of the Yozakura family. He is born on July 7, is between 15 and 16 years old, and stands 139 centimeters tall in his normal school form. When his mutated form activates, his height increases to 300 centimeters, and his appearance changes drastically. Nanao holds the Silver spy rank and specializes in hand-to-hand combat and the use of poisons. He obtained his spy license at the age of nine, and the event drew a crowd of 600 spectators, which left him deeply embarrassed. Nanao is a biochemical prodigy with exceptional knowledge of pharmacology and protein synthesis. He runs a research laboratory that spans four floors underground within the family home, where he develops medicines and treatments. He also assists victims of the government spy group known as the Hinagiku and maintains a professional rivalry with Dr. Mozu, a higher-ranking biologist. His unique ability, called Adaptation (or Immunity), allows him to neutralize toxins within his body and physically enhance himself, but the transformation is difficult to control. To attend high school alongside his sister Mutsumi and brother-in-law Taiyo, Nanao must take a powerful antidote to forcibly revert to his smaller childlike form. Personality-wise, Nanao is shy and easily flustered, and he strives to fit in with his family and classmates despite his extraordinary abilities. He is the only sibling younger than Taiyo, and he often looks up to Taiyo as an older brother figure, relying on him for guidance and support. Within the Yozakura family, Nanao serves as the medical and chemical expert, supporting his siblings during missions and treating their injuries. His character develops as he learns to better control his mutation and finds confidence in his role, while maintaining a strong bond with his family members, especially his brother Shinzo, with whom he frequently partners on missions.