Inspired by the manga and anime by Hideo Azuma.

Nana, is a young girl who unexpectedly acquires superpowers and at the same time loses her past memory as the unintended result of a scientific experiment gone awry. The mad scientist high school student who was running the experiment, Tomoshige Yotsuya, says he will help her regain her memories if she will join his detective agency. Nana innocently believes him, but Yotsuya's real intent is to use her powers to benefit his agency and himself.

The story unfolds as Nana encounters a variety of dangerous missions and mysterious events, but her natural sunny disposition helps her through all the incidents as she solves each mystery one after the other.