Born in Tokyo,[1] Imai won her first international medal at the 1992 Asian Junior Athletics Championships, finishing third behind Yoko Ota.

Imai broke the Japanese indoor record for the high jump in February 1998, winning in Beijing with a clearance of 1.91 m (6 ft 3 in).

[4] She jumped one centimetre lower at the 1998 IAAF World Cup to take fifth place for the Asian team.

[3] However, in December at the 1998 Asian Games it was Ota who topped the podium while Imai finished in joint fourth place, missing the bronze medal on countback.

[13][14] She failed to match this form at the 2001 World Championships in Athletics, recording only 1.85 m (6 ft 3⁄4 in) in the high jump qualifiers.

[10] She attempted but failed to clear Megumi Sato's outdoor Japanese record on four occasions that season.

She finally bettered that mark – which had stood since 1987 – with a jump of 1.96 m (6 ft 5 in) at the Super Meet in Yokohama.

[16] She was nominated for Japanese Athlete of the Year, but was beaten to the moniker by Koji Murofushi, who won a world championship medal and set an Asian record in the hammer throw.

[11] She cleared the same mark to beat Ota to the national title,[3] but failed to have a successful jump at the 2003 World Championships in Athletics.