In the year [[ExtyYearsFromNow 20XX]], violent crimes with heavy weapons have been rising at incredible rates. The Japanese police, unable to combat it all, has authorized a private police force known as... Private Police (Minkei in the original Japanese) to assist with certain difficult situations. One of these Private Police officers is Mikuru Nazume, a high-school girl/gunslinger who uses a special technique known as "[[GunFu Command Zero]]", or "[[TitleDrop Zero In]]" to achieve great success in the field, earning her the nickname "No-Murder Mikuru". While on a mission, she saves Kou Shiraishi, a classmate of hers and son of a well known detective, and helps him resolve to join the Private Police. Soon enough, he is assigned to Mikuru's squad and [[TheyFightCrime assists her in the field]].

Started in 2004, ''Zero In'' is an ongoing manga by Sora Inoue (formerly the illustrator of ''Manga/RealBoutHighSchool'') about Mikuru and Kou's work in the Private Police. Keep in mind, though, that crime-fighting isn't their whole lives -- both Mikuru and Kou are still very much [[OrdinaryHighSchoolStudent regular students]], just ones who work part-time as Rent-A-Cops. Really, ''really'' badass Rent-A-Cops.

!! This manga contains examples of:

* BadassInANiceSuit: Misono dresses exclusively in suits; she is also the most ruthless member of the team. Put it this way: she agreed to stop killing people about 10 chapters after her introduction...and she ''still'' has one of, if not ''the'', highest body count in the series.
* BreatherEpisode: Chapters focused on Mikuru and Kou's school life are usually much [[LighterAndSofter lighter and more comedic]] than the main bulk of the story, and tend to take place between more action-oriented arcs.
** Also, Chapter 30, a.k.a. the Ping-Pong chapter. [[CrowningMomentOfFunny Nothing more needs to be said.]]
* CaptainErsatz: Mikuru's mom is basically [[Manga/GunsmithCats Rally Vincent]].
* DarkAndTroubledPast: Mikuru, Kina, Misono...y'know, it might be shorter to list characters ''without'' one...
* DiabolusExMachina: [[spoiler:Kina finally gets some measure of revenge for her grandfather's killer, and is ready to move on and go back home to take care of her mother. Then she gets killed by a [[WhamEpisode stalker out of nowhere]], setting off a semi-[[HeroicBSOD BSOD]] for Mikuru and one of the more major arcs of the series.]]
* ExtyYearsFromNow[=/=]TwentyMinutesIntoTheFuture: 20XX, which doesn't seem too different from now, aside from the whole "exploding violent crime-rate" thing.
** Well, and that private gun ownership is apparently legal in Japan. And extremely advanced bulletproof armor that wears like leather.
* GunFu: Mikuru's "Command Zero" and "Zero In" in general, which was developed by her Grandfather and mastered by her Father.
* HappilyMarried: Nanami and her husband, as shown by an omake chapter. They have a 10-year old child.
* InsistentTerminology: Tomozou always calls himself "Ross", part his "Gun from LA" persona. No one else goes with it.
* LaserGuidedTykebomb: The witch was 16 when she killed the man who took care of her
* TheNicknamer: [[strike:[[InsistentTerminology Ross]]]] Hana Tomozou, who comes up with very odd nicknames for most people he meets. The most common one he uses is "Russian', for Misono, as she reminds him of a Russian Blue cat that his sister owns.
* NonActionGuy: Kou is classified as a "Keeper", which basically means he provides a support role. Extremely [[JustifiedTrope justified]] considering the number of actual fighters he works with, so he never has to be anything more than that.
* ObliviousToLove: Mikuru has no clue that Kou is in love with her. Kou in turn, is unaware of Noriko's feelings.
** Mikuru and Kou do realize their feelings in Volume 8 and 9
* OrdinaryHighSchoolStudent: Mikuru and Kou may be awesome Private Police officers, but they're still mainly students. [[spoiler: That ends after the School gets attacked.]]
* ShootTheHostage: Part of Misono's backstory. [[spoiler: When asked by her former colleague Yuki what she would do in a hostage situation, Misono claims that she would do this to get to the criminal. This is subverted when she is unable to do so when Yuki becomes a hostage, resulting in Yuki's death and Misono's insistence on unflinching bloodshed from then on.]]
* StalkerWithACrush: Played ''Horrifically''. [[spoiler:He makes dolls of those he's lusting after, then kills the person to "give his dolls life". He's responsible for Kina's death, abducts Kou's sister Ayuna, and is more or less the first serious BigBad in the series.]]
* TeamMom: Nanami, appropriately called "Leader". It helps that she's actually a mother outside her job.
* ThouShaltNotKill: A ''very'' big theme in the series. Mikuru believes this, and is able to enforce is with her skill, earning her the "No-Murder" nickname. Misono, on the other hand, does ''not'', which is the source of a lot of the [[TheRival feuding between the two]].
** [[spoiler:That being said, when Mikuru does snap she's liable to leave bodies around. They work very hard to make sure she doesn't.]]
* TrainingFromHell: The Minkei training.
* WhamEpisode:
** [[spoiler:Kina's death. The {{Foreshadowing}} is there, if you know where to look, but the act itself comes so quickly and unexpectedly that it still counts, especially cause it very forcibly jars the series out of its usually light tone and enforces a definite AnyoneCanDie feeling.]]
** [[spoiler: Mikuru and Kou get declared terrorists in Chapter 66 after they stumble into a plot by the Government to get a new reform going and get rid of Minkei by giving murders access to their equipment and framing them for the deaths of civilians.]]