Leonardo Da Vinci is a brilliant scientist and inventor from the Western Star, known throughout the series as the one who observes the world. He is a polymath and a leading figure in a renaissance that revives the advanced technology of lost prehistoric civilizations, including the Ikusa Yoroi, or Battle Armors. Driven by a deep curiosity and a desire to understand the universe, he holds a pragmatic and logical worldview, often serving as the voice of reason among the more impulsive protagonists. His primary motivation is to observe and guide the course of history, which leads him to accompany the visionary Jeanne Kaguya d’Arc on her journey to the Eastern Star in search of a prophesied Savior King. Upon arriving, he entrusts his self‑crafted Giant Battle Armor, which he names The Fool, to the reckless but charismatic warlord Nobunaga Oda, believing him to be the key to a new era. Leonardo becomes a close ally and advisor to Nobunaga, offering technological support, strategic counsel, and even a pocket watch as a token of their friendship. His personality is marked by a calm, analytical demeanor, a subtle wit, and a tendency toward sarcasm, though he is deeply loyal to his friends and fiercely protective of his inventions. He also uses a deck of Tarot cards to provide insight and guidance to those around him, interpreting their meanings with a detached but insightful wisdom. Throughout the story, Leonardo remains an observer‑participant: he does not seek power for himself but instead facilitates the rise of others, particularly Nobunaga, and works to ensure that ancient technology does not fall into the wrong hands. His role as a scientist and inventor is central to the plot, as the revival of the Battle Armors and Sacred Treasures reshapes the balance of power between the Western and Eastern Stars. His development is subtle, marked by a growing personal investment in the fates of his companions and a willingness to step beyond pure observation when the situation demands action. Notable abilities include his mastery of engineering and mechanics, his combat skills when piloting or defending his creations, and his broad knowledge of history and technology that makes him an indispensable strategist.