Fuuta is a young boy who ranks people by their abilities in a book half his own height. He has an extremely wide range of knowledge on thousands of people and is considered to be a valuable informant for the Mafia, sometimes being paid insane amounts of money for a copy of certain rankings, but due to this, he is often chased by the Mafia. When he ranks people, gravity around him becomes distorted, making objects around him float, and images of stars and galaxies appear in his eyes. It is unknown how he actually gathers his information, but his rankings do become skewed when it rains. He also has to be looking at the person to determine their rankings. He calls Tsuna his big brother, and starts living in his house.

In the future, after gathering information with Bianchi, Fuuta, who now carries a suitcase rather than a book, returns to Japan with crucial information about the Millefiore Family. Fuuta also reveals that he was Lambo's guardian until three years before Tsuna's arrival in the future, and prefers that Lambo not be endangered.

(Source: Wikipedia)