Matthieu Descartes, known in the Japanese version as Kanchi Imada, is a supporting character in the Yo-kai Watch franchise. He is a primary school student and the best friend and confidant of the main protagonist, Nathan Adams. Matthieu is characterized by his calm and composed demeanor; he is not shy but rather thoughtful, often acting as the logical and scientifically minded member of the group. He consistently seeks rational explanations for the strange events that occur around him, even though the supernatural yo-kai are the true cause. His motivations are simple: he values his friendship with Nathan and the other classmates, and he enjoys solving puzzles or mysteries through a practical, analytical lens. Within the story, Matthieu frequently appears in the background of everyday school life and serves as a grounding presence, occasionally participating in Nathan's adventures but never gaining the ability to see or interact with yo-kai himself. Key relationships include his close bond with Nathan, as well as friendship with other classmates such as Katie Forrester and Rémi Blaise. Over the course of the series, Matthieu undergoes minimal personal development; his primary function is to remain a steady, loyal friend who provides a contrasting worldview to the supernatural chaos. He does not possess any special abilities linked to the Yo-kai Watch, relying instead on his intellect and observational skills.