NB started out as a standard-issue helper robot assigned to Seina Yamada when he joined the G.P. Academy. Kiriko and Erma didn't trust Amane Kaunaq around Seina, so they had a video camera installed for surveillance purposes. But a short circuit from Amane's tinkering fried something important in NB's programming, completely warping its personality in the process.
So technically NB still functions as a helper robot, but now it's basically a voyeuristic pervert obsessed with catching girls undressing. It's rarely seen without its camera in hand, constantly scheming to get compromising shots. When the girls inevitably catch it in action—and they always do—NB ends up getting absolutely wrecked, dented and damaged every single time.
The name's actually a cheeky reference to Nabeshin, Shinichi Watanabe's character from Excel Saga and Puni Puni Poemy, which tracks given NB's ridiculous personality.
Content compiled by AnimeList.moe from publicly available sources.
