[4] In the near future, the Japanese National Police Agency covertly establishes an armed division called Minkei or Private Police in order to stamp out rampant crimes involving firearms by heavily armed criminals and terrorists.

Minkei's recruitment methods focus mainly on ability and as such is willing to take in anyone who displays the aptitude to handle the work.

Zero In follows the cases and interactions of the Light Knight B squad of Kou, Mikuru, Kina, Fujita, Hana and Shikie.

The story emphasizes Mikuru's developing relationship with Kou, her struggle to balance being a high school idol and a Minkei officer, and her physical rivalry with the older Shikie.

Over the course of the manga, Kou develops from a weak, bullied boy to a considerably popular and confident young man.