Fuuta is a young boy who ranks individuals based on their abilities using a book that is half his height. He possesses an extensive knowledge of thousands of people and serves as a valuable informant for the Mafia, often receiving substantial payments for copies of certain rankings. However, this makes him a target for pursuit by various Mafia groups. When Fuuta ranks someone, the gravity around him distorts, causing objects to float and images of stars and galaxies to appear in his eyes. The method by which he gathers his information remains a mystery, but his rankings become inaccurate when it rains. Additionally, he needs to see the person to determine their ranking. Fuuta refers to Tsuna as his big brother and begins living with him.
In the future, after gathering crucial information with Bianchi, Fuuta, now carrying a suitcase instead of a book, returns to Japan with vital data about the Millefiore Family. He also reveals that he was Lambo's guardian until three years before Tsuna's arrival in the future and prefers that Lambo not be put in danger.
