Originally, this was a standard helper robot that Seina was issued when he enrolled in the G.P. Academy. However, Kiriko and Erma, not trusting Amane with Seina, added a video camera for surveillance. However, a short circuit, caused by Amane's modifications had altered the personality of the robot.
Basically, NB's still the helper robot it was originally designed for, but now it has the personality of a voyeuristic pervert. NB is almost never found without its camera, hoping to catch girls in various stages of undress. However, the girls do catch it, the end result is NB getting dented. He is also terrified of NaBiko.
The name "NB" is a reference to Nabeshin, Shinichi Watanabe's character in Excel Saga and Puni Puni Poemi.