He also kicks a lot of ass in the movies. Notable examples include: him being turned into a dragon in the fourth movie and proceeding to kick his entire platoon's dragon asses. Note that when he transformed, Keroro, like the rest of his platoon, forgot all about his mission and who he was and while the audience were privy to the other platoon-turned-dragon members thoughts, we do not hear Keroro's at all.
In the third movie, Keroro engages his evil clone in a mecha duel to protect Fuyuki and holds on his own fairly well before he was downed. After reuniting with Fuyuki and finding Dark Keroro still alive, he angrily runs over and slaps the clone hard enough to send him flying.
Idiot Hero: Whenever he and his platoon are charged with saving Pekopon from other alien threats and not being the "threat" themselves.
Informed Ability: Supposedly a decorated war veteran, but (almost) never shows any of the competence and bravery you'd expect. A manga chapter eventually explaines why: Just before his first assignment, powerful aliens attacked and were obliterating Keron's forces. Keroro, unaware of all this, uses a port-a-potty which transforms into a space ship, takes off and single-handedly defeats the enemy, then lands. Completely oblivious to what just happened, he steps out to a hero's welcome and promotion to command of his squad.
Improbable Weapon User: In many video games, he draws from his collection of toys and cleaning supplies to help him out—the vacuum is a particular favorite.
The team's youngest member, made obvious by the fact he's still got tadpole features. Despite his cuteness, he's got a hair-trigger temper, a massive jealous streak, and likes firing his laser when provoked. Also, he loves his "Gunsou-san!"
Love at First Punch: He met Natsumi as he was trying to take over the Hinata house. She punched him so hard that his eyes were spinning in his head. Giroro fell in love with her as he fell to the floor.
The Worf Effect: Despite being the hard-boiled soldier who has a considerable reputation for martial prowess, Giroro often gets incapacitated by the current threat of the chapter/episode. This tends to occur before he could even fire a single bullet.
The team's intelligence officer. Incredibly smug and self-satisfied, Kururu is constantly inventing all sorts of weird stuff, but few of these are actually meant to help the invasion... they're just for his own amusement. Loves giving Keroro just enough rope to hang himself, over and over and over again.
Brilliant, but Lazy: If he isn't amused by what's going on, it requires either cash payment or physical coercion to make him actually expend effort for anything.
Pet the Dog: At times, actually shows signs of caring for others. One episode involved an actual puppy, complete with Natsumi and Fuyuki freaking out over what he might do to the poor thing.
A good example of the anime Flanderizing his character is their removal of two of his key moments during the Garuru Platoon's introduction: encouraging Keroro to keep resisting after losing contact with the others and opening a trap door underneath Keroro to force him to escape while he attempts to hold off Garuru armed with only his headphones. By contrast, Anime!Kururu simply retreats into his Hacker Cave, letting Keroro think he's abandoned him.
The team's token Ninja. Used to be a painfully shy, sickly child, and so clung rather desperately to his friendship with Keroro... something Keroro shamelessly exploited, leaving him traumatized to the point that any reminder of these abuses triggers his 'Trauma Switch' and sends him into the nearest corner. Grew up to become an assassin, then got separated from the others on Earth and found acceptance and peace with a group of ninjas, leading to him changing his name and outlook on life.
Ping Pong Na´vetÚ: In the anime, he often winds up asking "Keroro, are we really friends...?", yet never actually learns from his past experiences and is easily shocked back into his corner of woe by Keroro's latest transgression.
Powered Armor: The H-to-H Assassin suit (which bears more than a passing resemblance to Zoruru's enhancements...)
The Unfavorite: Thanks to being too nice for his team, he isn't always popular with his "friends"... assuming they notice/remember him. Extends to his portrayal within Keron Force media (such as being seated behind a plant during a news conference).
Even Natsumi is absolutely terrified of pushing Fuyuki too far, and Keroro, normally somewhat made of iron, was reduced to a stammering, terrified mess at whatever he did to him the first time this happened...
Chick Magnet: If it's female, and weird(Weird as in a schizo billion-heiress, an Emotionless Girl with a shape-shifting space entity on her head, and a mermaid) there's a huge chance they will have a thing for him.
Fuyuki's tomboyish older sister, she considers herself—correctly—to be the first line of defense against Keroro's taking over the planet. Has a massive crush on Mutsumi, and is good friends with Koyuki.
Action Girl: The platoon unilaterally considers her Earth's greatest warrior.
All Love Is Unrequited: Hopelessly crushes on Mutsumi, while getting crushed on by Giroro, Koyuki, several of her female classmates...
Badass Normal: She beat Giroro's web of booby traps armed with nothing but a stalk of leek during their first encounter.
Defrosting Ice Queen: She may still be suspicious of the Keronians in general, but she also seems to become a bit of a nicer character after they arrive—in addition to Giroro, she gets on pretty well with Koyuki.
Heir to a multi-billion-dollar international corporation, Momoka seems sweet and innocent at first, but has a hidden dark side related to her obsessive crush on Fuyuki. Spends tons of money on various Zany Schemes that she hopes will help her get closer to him, with little success.
A-Cup Angst: She couldn't help but be annoyed when she saw Natsumi and Aki (who both have better bodies) in bikinis.
Momoka's personal servant and Battle Butler. Always on hand to tend to her every need and slightest whim, no matter what it calls for. Also serves as a surrogate parent of sorts, as her parents are almost always off doing their own thing.
An extremely laid-back, smooth poet and artist who has an Odd Friendship with Kururu and serves as Natsumi's Love Interest. Runs his own radio show, and carries a special pen that lets him bring his drawings to life.
The Ace: In the few times he's seen in action, expect him to do it like a hardcore Badass.
Badass Normal: Aside from his pen, doesn't have any special abilities or skills.
The surprisingly cute Lord of Terror who was sent to destroy Earth as according to the prophecy of Nostradamus. Only she kind of missed her cue, and Keroro manages to convince her not to go through with it by virtue of being her beloved "Uncle". Sort of an honorary Sixth Ranger of the Keroro Platoon, though for obvious reasons she can't show off her moves all that often.
Dark-Skinned Blond: Her appearance deliberately invokes the 'kogal' trend; she based her human appearance off of a Deliquent girl she met once.
Did We Just Have Tea with Cthulhu?: The volume 19 of manga elaborate this. The Angols are beings from higher plan of existence, and while you can subdue them with Angol Stone, nobody understand what they really are. Keroro is the very first person who befriend the Angol.
Team Pet: An interesting inversion on the usual formula; instead of five humans with a ridiculously cute talking animal helper from space, it's five animals with a ridiculously cute talking human(oid) helper from space.
An old childhood friend of Keroro's, Kogoro is a Space Detective who always seems to be down on his luck. Despite this, he always seems cheerful, laughing and grinning no matter what he might be thinking.
Kogoro's younger sister, and the only one who can tell how he really feels at any given moment. As a result, she frequently has to act as a "translator" of sorts. Does her best to support her brother by taking various part-time jobs.
An Emotionless Girl adopted by the Shapeshifting alien Nebula, who rides around as her cat-eared headband and fights for her. He takes out her opponents and eats aliens, all while searching for a way to help her become human. Alisa, for her part, seems entirely uninterested in this... but shows some interest in Fuyuki.
The Chessmaster: May have been subtly manipulating the entire battle to make the Keroro Platoon look good. More obvious in the manga, where he explicitly spares Kururu's life and sends him to take on Tororo, which turns the tide of battle.
A cute, if insanely energetic, tadpole who absolutely adores his "Master Tamama"... And, rather obviously, was tapped to be part of the Garuru Platoon, where he cheerfully played Evil Counterpart to Tamama. Often puckers his lips up in a sort of "kissy face" expression.
Plot-Relevant Age-Up: Apparently hit Keronian puberty before Tamama, losing his tadpole looks. In the anime, this happens shortly after an episode involving him and Karara running around with Transformation Rays, including one that controls aging. Hmm...
Stealth Insult: His initial confrontation with Tamama during the Garuru Platoon's invasion of Earth is basically Taruru insulting his former idol in words of adoration and respect. It comes to a head when he stops calling Tamama "Sir" after he knocks him out.
A half-cybernectic assassin who appears to have joined the Garuru Platoon just to get a crack at Zeroro. Would probably love to be a Knight of Cerebus, if given the chance. Unfortunately, he tends to be even more forgotten than Dororo...
Artificial Limbs: A full half of his body, bisceted down the middle, has been replaced with robotics.
Failed a Spot Check: Like Dororo, ends up on the other end of this several times. One chapter plays with this, as he sits in on a meeting with the Keroro Platoon, taking Dororo's usual spot so that the reader's eye may glide right over him without seeing anything amiss... despite having just seen Dororo leaving with Koyuki. That's before the others take it Up to Eleven.
Freudian Excuse: Volume 17 of the manga revealed he apparently attended the same school as Keroro and Zeroro, and was completely ignored when those two first met... despite standing directly behind Zeroro at the time.
Knight of Cerebus: During the Garuru Platoon's invasion, he defeats and seemingly kills several of the Keroro Platoon's allies in rather nightmarish fashion, only to have this Subverted by an Anticlimax. Attempted again in Volume 17.
Unknown Rival: He's perfectly capable of being an excellent rival to Dororo... if he wasn't so forgettable that literally everyone stops noticing him with in seconds. He has to go out of his way to get people's notice.
Verbal Tic: Dramatic stammering, as in "Z... Zeroro..."
An incredibly irritating tadpole who hacked into Keron Forces' computer once, got caught and was promptly recruited. Considers himself Kururu's rival, and longs for the chance to put him through the ultimate Humiliation Conga.
Unknown Rival: Considers himself Kururu's rival; Kururu doesn't even remember him... And when he does, it doesn't end well for Tororo.
A Sixth Ranger of sorts for the Garuru Platoon's debut, with very different origins in the manga and anime. The manga version is a Creepy Child clone intended to "replace" Keroro, while the anime is a deaged, Brainwashed and Crazy Keroro.
Once an abandoned Keronian doll, Nuii was brought to life by Shurara and made into one of his agents. She had the ability to turn everyone into plush dolls like herself, and under Gyororo's supervision, inflitrated the Hinata household in the guise of Natsumi's old teddy bear.
Ambiguous Gender: There is heated debate as to whether Nuii is male or female, funny as it sounds.
Keroro's mother who first appeared in the KeroZero short shown before the 4th Movie. She's very loving toward her son like a good mother, but she also seems to have a tricky side to her.
Amazingly Embarrassing Parent: She just loves to go around and talk about how wonderful her son is while offering sweets. She does this to everyone, much to Keroro's chagrin.
Body Snatcher: Although Natsumi was the one who had the idea of switching bodies with her, with the consent of both, afterwards she just disappeared with Natsumi's body, going to sight see Pekopon and even on a date with Giroro (Even though he knew it was Keroro's mother) while Natsumi in her body got dragged to another city by Keroro's father, who didn't believe any switch had happened.
Giroro and Garuru's father. Appears to have a reputation just as terrifying as Keroro's father, though he's not mentioned as often. Makes a habit of turning even the simplest tasks into 'tests' for his sons.
Dororo's mother. Looksexactlylike her son (in a dress), and apparently passed down a lot of her personality traits, too. Whenever she sees Keroro, Giroro or Pururu, she immediately thanks them for being friends with Zeroro. Repeatedly. Over and over and over...
Voiced by: Junko Noda (Japanese) and Alison Viktorin (English)
An extremely cuteKeronian tadpole, Karara is an extremely naive daydreamer who dreams of finding her Knight in Shining Armor and falls in love at the drop of a hat with anyone who helps her out. Avoids Stalker with a Crush mainly because she runs off and does her "Bridal Training" offscreen, then shows up childishly expecting to have her affections returned...only to transfer her crush to someone else and start the whole process over again.
Ascended Extra: Appeared briefly in the manga; became a recurring character in the anime.
The Ojou: Same as her sister, though this generally isn't invoked as much for her.
Voiced by: Junichi Sugawara (Japanese)
An anime-exclusive character based on a fan submition, Joriri is an unshaven bum who appears in various flashbacks, giving the young Keroro, Giroro, Zeroro and Pururu questionable advice and generally being a poor role model. May have been introduced to add an "adult!Keroro" style character to the past, even though the younger Keroro already filled that role. Recently showed up in the present, much to the dismay of fandom.
Ascended Fanon: Joriri was originally one of the fan designs submitted to the Keroro Land mangazine, before being incorporated into the tv show.
Ice-Cream Koan: His big gimmick involves imparting an extremely odd form of sage wisdom that doesn't make a lot of sense.
Sixth Ranger: He joins the Keroro platoon in the 6th season... for one episode. Although that event is still referenced later.
Assassin Captain Jirara
Voiced by: Kouji Yada (Japanese)
Leader of the X1 assassin troop on Keron, and Zeroro's trainer in the art of killing. Cold and merciless and wanted in several galaxies, it only makes sense that he popped up on Pekopon...
Artificial Limbs: It almost seems like this is a requirement for spooky assassin-types.
Drill Sergeant Nasty/Sadist Teacher: Jirara trains his underlings by making them constantly fight each other nearly to the death. If you die, you were a bad student anyways.
However, a Flashback in Volume 17 of the manga reveals that he deliberately chose a Lighter and Softer alternative to making Zeroro a full-fledged assassin, despite acknowledging that Zeroro had excelled in his training. When his pupil begged for an explanation, Jirara tells him flat-out that the assassin's path is "darker than you can even imagine".
Another character solely from the anime. Despite his rank and the respect he apparently has, he's very... Crazy. Most of this is put in the direction of his unhealthy infatuation with Pururu. Really, really unhealthy.
An alien race of humanoid snakemen, the Vipers are natural enemies of Keronians and are dangerous, deadly predators. Most of the Vipers that show up in the anime have a personal vendetta against the Keroro Platoon, thanks to what happened to the first Viper that targeted them. In the manga, on the other hand...
A sort of ancient Keronian super weapon that feeds off of negative emotions to gain strength and destroy planets. While not necessarily movie exclusive, they're a very big element of the first and third movies, and become a victim of the Worf Effect in the second. In the first movie, Keroro and Fuyuki accidentally unleash one on Tokyo.
An ancient Keronian weapons specialist that sealed away the first Kiruru, but got stuck in the proverbial can with him as well. She works off of positive emotions, and is able to turn into a key, the only thing that can reseal the Kiruru and save the world.
Reset Button / Status Quo Is God: The plot couldn't allow the Keroro Platoon access to knowledge of ancient Keronian technology, as it might have allowed them to conquer Earth, especially as she was getting along with Kururu. So of course something happens to her by the end of the movie.
Senseless Sacrifice: By the 2nd movie it's shown that the Maronians can easily take out a Kiruru, so vanishing to seal it up is more or less pointless as a long-term solution.
A Maronian living at the bottom of the ocean who was feeling lonely one day and as a result, abducted Natsumi to be his princess. In the end, all he wanted was a mother figure rather than a princess.
The primary antagonist of the third movie. Cloned from a sample of Keroro's own DNA, taken off the Kero Ball when it was lost in an ancient Keronian facility hidden in the ancient city of Macchu Picchu in Peru.
Homage: to Sun Wukong of the Journey To The West tale that Dragon Ball was based on. Note his 'symbol', which is really a band around him that resembles the flying cloud, while resembling Wukong's Restraining Bolt. He even uses the original 'Great Saint That Surpasses Heaven' title when he first appears.
He's also a pretty direct reference to Goku from Dragon Ball. He uses a blue blast of energy at one point charged up similarly to the Kamehameha and, in the final battle, attempts to use the Genki Dama while fighting against Tamama and Momoka, even calling up for other people's power. One of the scenes featuring him in the credits sequence is a homage to Dragonball's original ending and another one shows him in a place very similar to the Tenkaichi Budokai tournament from Dragonball, fighting against someone with the body obscured, but wearing pants and shoes identical to Yamcha's in the 22nd and 23rd Budokais.
One of Momoka's old friends, and shares a lot in common with her - except that her rich parents passed away early on. All she wanted was a real family, and from the depths of Mont-Saint-Michel, someone answered...
When Shion attempts to breed the Earth Dragon egg hidden under Mont-Saint-Michel, the plan reaches frution and the massive Earth Dragon is hatched - but the destruction it causes to the world forces Shion to intervene, and eventually the Earth Dragon relinquishes its power, turning into a harmless little creature that resembles a salamander-based Keronian.