The story is about the adventures of a 14-year-old girl named Nico Hayashi, who uses her talents of changing and altering her voice to manipulate men over the phone who want to participate in enjo kōsai.

While Nico is on her first case, she meets with a geeky man named Iichiro Sudo, who has an obsession with robot toy models.

After completing her first case Nico proclaims herself "Sexy Voice" and a variety of short loosely linked character-driven adventures ensue.

[10] An 11-episode Japanese television drama, starring Kenichi Matsuyama as Robo and Suzuka Ohgo as Nico, was broadcast on Nippon TV from April 10 to June 19, 2007.

[11][12] Sexy Voice and Robo won the Grand Prize of the Manga Division at the sixth Japan Media Arts Festival in 2002.