Keroro

The story began with a one-shot titled Keroro Gunso in 1998.

Full serialization started in the April 1999 issue of *Monthly Shonen Ace*.

The collected volumes reached 35 volumes as of December 2025.

By June 2018, the series had surpassed 14 million copies in circulation.

Past chapters were also reprinted in the magazines *Keroro Land* and *Kerokero Ace*.

*Keroro Land* additionally featured original newly drawn comics.

The core theme of the work is family.

Its main comic engine comes from the clash between ordinary domestic life and absurd alien invasion plans.

An advance invasion unit from Planet Keron arrives on Earth, which aliens in the series usually call Pekopon or Pokopen.

The squad is led by Sergeant Keroro, joined by Private Second Class Tamama, Corporal Giroro, Sergeant Major Kururu, and Lance Corporal Dororo.

Things go wrong immediately.

The five soldiers are separated during landing, and Keroro is quickly discovered and captured by Natsumi Hinata and her younger brother Fuyuki Hinata.

The Keronian main force judges the situation too risky and retreats, abandoning the advance team on Earth.

Keroro ends up living in the Hinata household, where he spends as much time cleaning and building model kits as he does plotting conquest.

As the story continues, the scattered squad members reunite one by one.

Soon even Angol Mois, a girl from the allied Angol race, begins living with the Hinatas, making the household even more chaotic.

The basic pattern is simple and very funny.

Keroro and his squad devise a new plan to conquer Earth, only for the plan to collapse through bad luck, poor execution, or a beatdown from Natsumi.

Even with its invasion setup, the series is warm rather than grim.

As the manga progresses, the bond between the Keronians and the humans becomes one of friendship as much as conflict.

Most chapters are self-contained.

However, some storylines run across two to four chapters and occasionally even span multiple volumes.

The manga is also famous for its heavy use of parody, homage, and borrowed visual or verbal references from other works.

That tendency carried strongly into the anime adaptation as well.

The original manga also contains a notable amount of fanservice.

Alongside the slapstick and family comedy, it includes many appealing female characters and playful romantic elements.

Keroro Squad

Sergeant Keroro is the protagonist.

He is the leader of the Keroro Platoon, an alien invasion unit from Planet Keron, but he quickly becomes more of a freeloading houseguest than a conqueror.

Private Second Class Tamama idolizes Keroro and calls himself the squad’s mascot.

He usually acts cute and lovable, but when angered he becomes wildly dangerous.

Corporal Giroro is Keroro’s serious and battle-hardened childhood friend.

He is committed to the invasion mission and constantly loses patience with Keroro’s laziness.

Sergeant Major Kururu is a genius inventor who delights in pranks and psychological warfare.

He creates all kinds of bizarre machines and often embraces the role of the squad’s resident troublemaker.

Lance Corporal Dororo, formerly known as Zeroro, is a ninja-like Keronian who loves Earth deeply.

Although he distances himself from the rest of the platoon, he still remains connected to Keroro and Giroro as an old friend.

Hinata Family and Human Allies

Natsumi Hinata is the main heroine.

A middle school girl living in the Hinata house, she repeatedly crushes the Keroro Platoon’s schemes with force and confidence.

Fuyuki Hinata is Natsumi’s younger brother and an occult enthusiast.

Kind and open-minded, he treats aliens with curiosity rather than fear and wants to be Keroro’s friend.

Aki Hinata is the mother of Natsumi and Fuyuki and head of the household.

She works as the editor-in-chief of a manga magazine and handles the absurdity around her with remarkable ease.

Momoka Nishizawa is Fuyuki’s classmate and heir to the vast Nishizawa conglomerate.

She lets Tamama stay with her and is portrayed as a girl with both a public gentle side and a far more intense private one.

Mutsumi Hokushiro, also known as 623, is Kururu’s partner.

He is a mysterious and cool young man who is publicly active as an entertainer but has an unclear background.

Koyuki Azumaya is a girl from the former ninja village of Shinobu.

She stays close to Dororo, who once saved her, and later becomes friends with Natsumi after transferring schools.

Other Key Characters

Alisa Southerncross is a girl who hunts dark beings called Dark Wraiths that threaten planets.

She was originally a doll, but gained self-awareness through the actions of Nebula, whom she calls “Daddy.”

Angol Mois is a girl from the humanoid Angol race, allied with Keron.

Although she is supposed to destroy Earth, she never quite goes through with it and quietly carries feelings for Keroro.

New Keroro is a younger Keronian sent to invade Earth in place of the original platoon.

He is pure-hearted, energetic, and still inexperienced.

Earth

In the series, aliens call Earth Pokopen or Pekopon.

Many adaptations preferred Pekopon because Pokopen was considered sensitive broadcast language.

To many aliens, Earth is treated as a provincial backwater.

At the same time, its culture is admired, and traces of alien activity are said to exist in ancient ruins and hidden modern facilities.

Even in the present era of the story, hidden alien districts and space railway stations exist around the world.

These places are often visited by extraterrestrial travelers.

Planet Keron

Planet Keron is the 58th planet of the Gama Nebula.

It is the home world of the Keronians and is depicted as a green world with star-shaped cloud patterns.

Its humidity is higher than Earth’s.

Its environment resembles Earth in some ways, though it lacks oceans of seawater.

Time flows differently there.

In volume 22 of the manga, 300 years have passed on Keron since the platoon came to Earth.

Keronians

Keronians are the dominant intelligent species of Planet Keron.

They are small, frog-like beings with elastic bodies and a preference for humid conditions.

Their everyday physical ability is not too different from that of humans.

However, they possess high latent potential.

Keronian Army

The Keroro Platoon belongs to the Keronian Army.

Its headquarters is the central mothership Grand Star, and transportation to headquarters is available from Planet Keron.

The army uses a rank system broadly similar to that of the Japanese Army.

There is also a military academy where Keroro and the others received training.

Despite being a proper military force with invasion campaigns and superweapon development, it is also oddly goofy.

Its orders can be theatrical, and squad leaders may even be assigned tasks that look like elementary school homework.

Resonance

Resonance is an action used by the Keroro Platoon to raise morale.

According to Pururu, it contains a hidden power that the squad originally did not understand well enough to use properly.

In the manga, Dororo does not participate in Resonance at all from his first appearance in chapter 55 through chapter 164.

In the anime, by contrast, the full squad uses it and produces effects ranging from better cooking to impossible quantities of dumplings.

Anti-Barrier

The Anti-Barrier is a device used by aliens to become invisible.

It is usually used against humans, and can be adjusted so that only selected targets are able to see the user.

Curiously, it does not work on especially curious people.

Its name does not mean “anti-barrier” in the usual English sense, but refers to a “safe zone barrier.”

Keroball

The Keroball is a multifunctional device issued only to squad leaders in the Keronian Army.

It has communication functions and many other abilities, and its usage fees are billed afterward.

Although it is assigned to Keroro, it is currently kept by Fuyuki.

Both Fuyuki and Keroro use it without always asking permission.

Keron Star

The star-shaped emblem on Keroro’s abdomen is called the Keron Star.

It serves as proof of command and grants the authority and dignity of a leader.

It cannot be copied or erased and is considered a military secret.

Exactly why a screwup like Keroro received one remains unclear.

The Military Confidential Archive is installed in Keroro’s Keron Star.

It contains the complete historical data of the Keronian military.

The Rebuild Keron Star belongs to New Keroro.

It is mainly used to store his combat data and change his battle style settings.

The Turn Keron Star belongs to Black Star and is effectively Black Star’s true body.

It is itself a military archive and contains immense stored data, though no new data can be added to it.

Underground Base

The Keroro Platoon’s headquarters is an underground secret base beneath the Hinata house.

Access is normally through a refrigerator-shaped warp device in Keroro’s room.

Because the base is expanded carelessly over time, it becomes more like an anthill than a proper fortress.

For a secret base, it is hilariously easy for both aliens and humans to break into.

Space Police

The Space Police monitor and police alien activity in outer space and on planets.

Their authority is portrayed as so overwhelming that even the Nishizawa Group and the Keronian Army are beneath them.

They are notorious for rough methods and a “detain first, ask later” mentality.

In the manga, the only confirmed officers are Poyon and Poyan.

Alien Districts and “Space” Products

Alien Districts are hidden urban zones closed to ordinary humans.

They are divided into Side 1 through Side 6, with Side 6 located beneath a shopping district in central Oku Tokyo City and even capable of transforming into a robot.

The prefix Space- is attached to many nouns in the setting to mark them as extraterrestrial.

Sometimes these things are almost identical to Earth products, and sometimes they are completely bizarre.

One unusual trait of *Sgt. Frog* is that some ideas created first for the anime were later adopted by the manga.

This reverse flow of adaptation became part of the franchise’s charm.

Examples include characters such as Nyororo, Karara, Sylvie, Poyan, Satsuki Shiwasu, Yayoi Shimotsuki, Pururu, Captain Jirara, and Aku Aku.

In some cases, the manga version altered names, details, or backstory.

Other anime-origin concepts that entered the manga include the Occult Club, Nishizawa Tower, Keroro’s verbal tic “gerogerori”, and the setting element Oku Tokyo City.

Keroro’s catchphrase in particular began as an ad-lib by voice actor Kumiko Watanabe.

Main Manga

The manga is written and illustrated by Mine Yoshizaki.

It was published first by Kadokawa Shoten and later by Kadokawa under the Kadokawa Comics Ace label.

Volume 1 was released in November 1999.

Volume 35 was released on December 26, 2025.

Spin-off Manga

A spin-off titled Sgt. Frog Special Training: Great Battle on the Warring States Planet was created by Yumeta.

It ran in *Kerokero Ace* from 2007 to 2009 and was collected in 3 volumes.

Another spin-off, Keroro Pirates: Sgt. Frog Special Training: The Treasure of the Great Voyager Star, was created by Akiru Otsuki.

It was also published in *Kerokero Ace* and collected in 3 volumes.

Special Edited Volumes

Several themed compilation books were released.

These include Green, Red, Pink, Yellow, and Black, each collecting chapters around specific themes or characters.

Guidebooks

Official companion books include Volume 11.5 Official Guidebook, Secret Super Encyclopedia, and K-File Official Guidebook 22.5.

These books contain character profiles, mechanical notes, interviews, extra illustrations, and bonus manga.

A package labeled Volume 25.5 included an anime DVD.

It collected selected episodes of the flash anime along with manga material and storyboards.

Musha Kero

Musha Kero is the umbrella label for franchise works inspired by samurai, the Sengoku period, and Musha Gundam imagery.

It grew from a visual motif that became popular enough to expand into its own branch of the franchise.

Keroro Pirates

Keroro Pirates covers works in the franchise built around pirate motifs.

It is one of several themed sub-brands developed from the larger property.

Keroro Quest

Keroro Quest groups works with a fantasy role-playing flavor, especially western knight imagery.

Along with Musha Kero and Keroro Pirates, it also appeared in the background imagery of an anime ending theme.

Keroro Land

Keroro Land was a children’s magazine devoted to the franchise.

It functioned as a special issue line connected to *Monthly Shonen Ace*.

Television Anime

A television anime adaptation of Sgt. Frog aired on TV Tokyo and affiliated stations from April 2004 to April 2011.

A related series, Sgt. Frog Otsu, aired from April 2010 to April 2011 on TV Tokyo.

Both were produced by Sunrise.

The anime became one of the franchise’s defining successes and greatly broadened its audience.

Theatrical Anime

The theatrical branch included five feature-length films and three short films.

These were produced within the same overall creative system as the television anime.

Flash Anime

A short-form flash anime titled simply Keroro aired on Animax from March to September 2014.

It was produced by Sunrise and Gathering.

Before serialization, a one-shot version titled Keroro Gunso appeared in 1998.

Chapter 226 of the later manga established it as a prequel to the serialized first chapter.

One-Shot Plot

In the one-shot, a mysterious tadpole sent from the countryside for a summer homework assignment grows into Keroro.

He turns out to be an alien who had been rescued when he collapsed, and he tries to repay the favor under his planet’s rule of returning good deeds with “results.”

At the same time, he is on Earth for his own summer homework: observing humans.

The setup is close to the later series, but clearly rougher and more experimental.

Main Differences

Natsumi appears there under the spelling Natsumi but is a sixth-grade elementary student rather than a middle schooler.

The one-shot also mentions that she is “in her growth phase.”

Keroro has an alternate name, Batrakos.

Later, chapter 226 explains this as the designation of a reconnaissance unit carrying Sergeant Keroro’s personality operating system.

A game-loving bespectacled girl named Mariko also appears in the one-shot.

She does not become part of the regular serialized cast.

Other Early Character Concepts

An earlier planning stage featured different human partners for the Keronian characters.

These concepts were documented in the official guidebook material.

Jun Yamato was the prototype for Natsumi.

She was an ordinary but suspicious girl who liked sports and belonged to the handball club at Hinomaru Girls Middle School.

Chinatsu Yahagi was Jun’s rival.

Her partner was Corporal Kekero, an early form of Giroro with different markings, camouflage on his hat, visible body scars, and a dialectal speaking style.

Haruna Hamakaze was an unpublished prototype character.

She wore glasses, had messy bedhead hair, and was an otaku girl interested in manga, games, anime, and radio.

Her partner was Sergeant Major Rororo, an early Kururu-type character.

He lacked Kururu’s chest mark, wore a headset with a microphone, and spoke in a more clipped manner.

Fuyumi Yukikaze was another unpublished concept.

She was presented as a glamorous older-sister type and leader of a street-racing group.

Her partner was Private Roroke, an early Tamama-type character.

Aside from a pink hat and a somewhat larger tail, he was not very different from the later version.

Akie Asagiri was a prototype corresponding to the later ghost girl Okanoe.

Her partner was Sergeant Rokeke, an early Dororo-type with a different hat shape, a more mechanical mask, and a wetsuit-like outfit.

The manga was selected as a recommended work by the jury of the 11th Japan Media Arts Festival in the manga division.

Its success also led to many cross-promotional appearances and industry references.

When the work won the Shogakukan Manga Award, some media outlets mistakenly called it Keroro Shogun instead of Keroro Gunso.

Yoshizaki responded by drawing a celebratory “Keroro Shogun” illustration, complete with armor and war fan.

That image later appeared in multiple franchise contexts.

It also helped inspire the later Musha Kero branch.

Mechanical designer Hajime Katoki contributed to limited-edition comic packaging, weapon designs for Natsumi’s powered suit, featured mecha projects in *Keroro Land*, and even anime storyboards.

This happened partly because Yoshizaki was a fan of Katoki’s work.

For the film Little Braves: Gamera, Yoshizaki drew the cover of the then-unreleased volume 13 for use in the movie.

This was based on his love of Gamera and on the film protagonist being a fan of *Sgt. Frog*.

The series also inspired tie-ins and exhibitions in Kumamoto, where Yoshizaki spent his elementary and middle school years.

These included an original art exhibition, a themed city event, and decorated streetcar promotions.

Seibu Railway later used the characters for a long-running manners campaign titled Operation Invade Seibu Railway with Sgt. Frog Manners.

That campaign ran from 2010 until it was effectively replaced in 2015.

The franchise has appeared in or been referenced by many other manga, anime, games, dramas, and live events.

Its strong parody identity made it especially easy to borrow and be borrowed by other pop culture works.

References or appearances have been noted in works such as Train Man, .hack//G.U. Vol. 1: Rebirth, Gintama, Bobobo-bo Bo-bobo, The Life of Jii-san, Hayate the Combat Butler, Lucky Star, Code Geass: Lelouch of the Rebellion R2, Paco and the Magical Book, and The Case Files of a Female College Accountant.

The franchise also had a notable connection with the Tales game series.

In the PlayStation 3 version of Tales of Vesperia, the character Karol can gain a Sergeant Keroro costume title, and his battle voice lines shift toward Keroro-style delivery because both are voiced by Kumiko Watanabe.

A collaboration illustration was also included as a preorder bonus for Keroro RPG: The Knight, the Warrior and the Legendary Pirate.

It paired Keroro Platoon members with *Tales* characters voiced by the same actors.

A playful self-parody spirit even appears through voice casting links.

For example, jokes in crossover material draw on the performances of Kumiko Watanabe, Etsuko Kozakura, Jouji Nakata, Chiwa Saitou, Takehito Koyasu, and Takeshi Kusao.

In North America, the title was released as Sgt. Frog.

The manga was published by TokyoPop, and the cover art differed from the Japanese edition.

In South Korea, the title became Sergeant Keroro the Frog in translation.

The setting was localized to Korea, and several human character names were changed, while the five Keroro Platoon names remained the same.

In France, the first anime season aired as Keroro, Mission Titar, and later episodes used the title Keroro.

Some human characters also received localized names.

In Spain, the on-screen opening used SGT Keroro, while the broader series title was Sergeant Keroro in Spanish.

These international releases helped the series build a lasting global cult following.