- "The World may be virtual, but those people are real!"
- — Kazu —
Kazu is a young, brown-haired boy. A Wavemaster, he is dressed in white robes decorated with his wave pattern, and carries a small messenger bag on his left shoulder.
Kazu acts fairly goofy in the game. He is especially fond of randomly choosing dungeons then trying to clear them, regardless of their level. Luckily he is fairly powerful and a quick thinker, so he is usually able to avoid trouble. He is protective of those he considers friends, and will do all he can to help them even at risk to himself.
Offline, Kazu is Fumikazu Hayami, a junior high student. He lives with his parents, his older sister Akira, and his younger brother Kouta. The Kunisaki twins Shugo and Rena used to live in the same apartment building as him, but they moved away shortly after the game series ended.
Aside from playing The World, Fumikazu likes playing with animals. Especially his pet prairie dog, Hana.
In Another Birth, Kazu obessively plays The World and one day, has his sister, Akira, choose an area for him while she was telling him that it was dinner time. She chooses Δ Hidden Forbidden Holy Ground, and then leaves to the kitchen. After a few minutes, Akira and her mother hear a thud in Kazu's room and find him unconscious. He is then taken to the hospital and is found out that he became comatose.
Fumikazu recorded a journal entry of his exploits in The World. In it, it is revealed that he met a variety of characters including Sieg, Akira's friends Shouko and Yuuji (using their avatars Syua and Mac), and once spotted the Descendants of Fianna although he didn't have the courage to speak to them. He also had a close relationship with a Blademaster girl named Haru.
Kazu doesn't appear in the .hack//Games until the very end, but he is the primary driving force for solving the mystery in the world for one of the major characters. He is to BlackRose what Orca is to Kite. He makes an appearance at the very end, along with other known characters, to assist in breaking Corbenik's shield. After waking up, BlackRose tries to stop him from playing the game, but he is later found by Kite and admits that he is connecting from an internet cafe.
In the manga, Kazu knows Rena and Shugo in the real world- he and Akira were their next-door neighbours. He is the main reason that Rena decided to play The World. Shugo played under Kazu's name one day and met Aura. Shugo told her that he wanted to be a hero one day. Kazu helps Shugo escape from Kamui at Δ Hidden Forbidden Holy Ground and gives Shugo the Helba Key to access Net Slum. Kazu then helps Ouka fight Magi to prevent her from reaching Shugo.
- It's possible that Kazu and Ouka started dating following the events of Legend of the Twilight, though their relationship was probably kept within The World.
- Tokyopop mispelled his name as "Kaz" throughout volume 3 of the Legend of the Twilight manga.