Genryūsai is a founding member and elder of the World Ninja Association (WNA), dedicated to preserving ninja heritage. As a legendary ninja, he maintains a calm and laid-back demeanor in everyday life. He leads young ninja students investigating extraterrestrial threats known as Space Ninjas, gum-like aliens that absorb ninja DNA to grow stronger.

His mentorship becomes significant after a housefire injures Van's father. Genryūsai takes responsibility for training Van, guiding him to hone his awakened ninjutsu abilities and supporting Van's nighttime vigilante activities against the Space Ninjas. This relationship is explored in the story mode's first chapter, where Genryūsai serves as a patient instructor during Van's battles.

Genryūsai is the twin brother of Gen'unsai, Kappei's grandfather. Both are respected figures, but Genryūsai is more reserved and quiet compared to his brother. Their responsibilities differ: Genryūsai primarily operates within the WNA in Komerica, mentoring multiple young ninjas including Burton and his peers, while Gen'unsai oversees traditions in their ancestral home of Oedo.

His involvement extends beyond individual training to broader WNA initiatives countering existential threats like the Space Ninjas and internal conspiracies within the organization.