Over the course of the 2007 season, Kazuki covered over 7,000 km for the AT&T Williams team as a test driver, as well as representing the team at Grands Prix as a driver in the Friday practice sessions. He closed the season with a capable Formula One debut, racing for the team at the Brazilian Grand Prix at Interlagos.
After that race, it was announced that the Japanese driver would be the team's second driver for 2008, partnering with Nico Rosberg.
Kazuki, the GP2 Series Rookie of the Year, was previously a member of the Toyota Driver's Program since 2003 when he claimed the Formula Toyota Championship. He also contested the All Japan Formula 3 Championship and the Formula 3 Euroseries.
