A kindhearted and sophisticated teenage boy. Kio is easily able to accept the proof that his new friend is an alien, and that both his other friends are secret agents. He knows how to handle firearms, though he is not sure what business his Uncle Yuichi is in to have them. He displays a strong sense of justice, and is willing to take action when he feels it is needed. This sense, and his treatment of others, draws the attention of his female friends. He is unsure about his reaction to all that interest, and their attention begins to cause complications for Kio. Eris the Catian in particular has decided that she wishes to be his mate as she is about to come into her first heat.
- Adorkable: Manami calls him an otaku, but the other girls point to her that it's a part of his charm.
- Alliterative Name: Kio Kakazu.
- Can't Hold His Liquor: In the first episode, he passes out from taking a sip of beer (though it's implied that he remained conscious for a while after, he's unable to remember anything after that point).
- The Cassandra: His beliefs that the Catians are a real humanoid race are dismissed by Manami and Itokazu, but it later turns out to be true.
- Leotard of Power: Gets one of his own in the last stretch of the series. It's just as thin, tight, and clingy as the ones the Catians wear, it's just full-body.
- Non-Action Guy: Considering most of the main girls around him fall readily into Action Girl territory, he's more or less The Heart for the team.
- Oblivious to Love: Despite Eris spending the first half of the series literally and directly saying she likes him and wants to have sex with him, he seems to forget all about it the moment she stops being in heat. Considering how freaked out he was by her overt actions, this is probably deliberate on his part.
- Porn Stash: Kio has a few magazines. Not very secret, though, as even Manami knows where they are. And Eris keeps finding them... and using them as cultural references.
- Took a Level in Badass: Kio, who goes from 'standard-model Unlucky Everydude' to 'capable of tearing apart a Humongous Mecha with his bare hands' after getting his own suit of Powered Armour. The rest of the cast were suitably astonished.
A 16-year-old scout for the Catian people exploring Earth. Tall and well endowed, she has easily befriended many people, and regular cats she has met on Earth. Initially most do not believe her to be an alien, but she shows Kio the proof directly with her technology, ears and tail. While she is learning the ways of Earth, she is also a competent fighter who employs strategies and technologies not seen on Earth. Her interactions with Kio are closer and more emotional, potentially due to the fact she is 16 and about to enter her first heat. With the kindness and interest he has shown, she has selected him as a mate. Her first heat was forcibly ended by pills as it was causing disruption to her duties as an ambassador and representative of Catians on Earth.
- Beware the Nice Ones: Despite being the happy-go-lucky Cat Girl Eris happens to be, she is definitely not one of those characters you would want to frustrate.
- Bi the Way: When under the influence, anyway. She's more than willing to kiss Manami for more catnip.
- Boldly Coming: After making first contact with humanity, she wants to make a lot more contact with Kio.
- Boobs of Steel: Not only is she well-endowed, but even though it's her power suit that gives her the strength, she had no problem subduing her kidnappers in episode 2 of the anime.
- Cat Girl: As with all Catians, she has cat ears and a tail.
- Dissonant Serenity: In episode 2, Eris sweetly tells a government agent that she will beat the utter crap out of him and his cronies after she confirms that they are in league with dog aliens. She even cracks her knuckles with a smile on her face.
- Expressive Ears
- Gag Boobs: All the human female characters she meets in the first episode freak out over the size of her breasts.
- Genki Girl: A continually cheerful Cat Girl. She's nearly always smiling and having fun.
- Innocent Fanservice Girl: Eris sees no problem walking around the house in a partially-buttoned shirt/pair of panties and nothing else, or with joining Kio in the bathroom while they're both naked. She also mistakenly thought that wearing schoolgirl swimsuits to a meeting was an Earth-custom, due to Kio's often misleading Porn Stash.
- Leitmotif: One of the three primary closing themes of the show, Happy Sunshine.
- Magical Girlfriend: Before he met her, Kio was a geek living a quiet life in Okinawa. Once he encounters Eris, a Cat Girl alien who's arrived to open relations with Earth, Kio's home is turned into the "Catian" embassy. Two of Kio's classmates even sum it up by saying that being in a relationship with her would be like "winning the nerd lottery" for Kio.
- Meaningful Name: In Greek mythology, Eris was the goddess of chaos whose actions indirectly started the Trojan War. In this show, Eris is a Cat Girl alien whose very presence causes several secret societies and black ops organizations to come gunning for her all at once.
- Nice Girl: Courteous, respectful and friendly to just about everyone. Along with her cheerfulness, this wins her plenty of friends. When Aoi breaks down and gives her "The Reason You Suck" Speech, Eris's reaction is to give her a hug and try to make her feel better.
- Rapunzel Hair: Her long hair reaches down to her waist.
A teenage girl who worked for the Immigration Bureau of Japan as one of their top agents before helping save Eris. She is now seen as a traitor so she lives at the Catian Embassy under its diplomatic immunity. She has the ability to teleport objects to her that lie within a 50m radius. She also makes use of a technologically advanced battlesuit and weaponry, (unknowingly provided by the Dogisians).
- A-Cup Angst: Always feels inferior towards other girls when she's not in Action Girl mode because of this, particularly around Eris.
- Blade on a Stick: In the anime.
- Cool Car: Her Ford Shelby GT500, outfitted with defensive "spy car" gadgets.
- Cursed with Awesome: She tells Manami that she has the ability to teleport objects within 50 meters to her. But apparently this ability caused her parents to abandon her.
- Cute Bruiser: Especially when she's wearing her suit, or later, Ichika's scrolls.
- First Kiss: Kisses Kio first during the Now or Never Kiss.
- Goggles Do Something Unusual: Only shown once though, when she spotted an infrared Laser Sight from a sniper that is otherwise invisible to naked eye..
- Guns Akimbo: She uses two pistols in several fights, though not always.
- The Gunslinger: Of the trick shot variety. She is by far the best shot of any of the main characters.
- Half-Human Hybrid: Maybe. Her sister is, but Aoi may just be a mutant.
- Hyperspace Arsenal: Justified with her ability to warp any object within 50 meters.
- Improbable Aiming Skills: The most spectacular example probably being when she neutralizes a sniper round aimed at Manami by shooting her with an anti-matter bullet, at exactly the right time and placement for the clothing-erasing effect to absorb the shot.
- Normally, I Would Be Dead Now: Aoi should probably have been crippled or killed after she fell out of the moving subway car, but she didn't even end up with any bruises or abrasions other than some scrapes on her left arm when she stood up immediately after getting kicked off. Her fast recovery is noticed later on.
- Parental Abandonment: Aoi's parents kicked her out after finding out about her apporting abilities. There might be more to the reasons why her parents left her behind if the DIA file on her from Episode 3 is accurate.
- Psychic Powers: She's an Apporter.
- Rapunzel Hair: She has long flowing hair that reaches to her waist.
- Teleportation: She has the ability to teleport objects within 50 meters to her.
- Tomboy and Girly Girl: The Girly Girl to Manami's Tomboy.
A tomboy, childhood friend, and next door neighbor of Kio. Since she was young she wanted to join the CIA, where her room is filled with listening equipment and guns. She was in the CIA recruitment program operating under the supervisor codenamed JACK, but thinks that she is no longer a candidate after helping rescue Eris. She also lives at the Catian Embassy under its diplomatic immunity.
- Badass Normal: She's an ordinary human without Aoi's apportation or Eris' technology. She's just good with a gun, and she fights alongside the rest of the Battle Harem with no problem.
- Boobs of Steel: Unlike Eris, whose power suit gives her the strength, well-endowed Manami doesn't need a power suit to engage in combat, or, unfortunately, to beat up Kio.
- Childhood Friend Romance: She has a crush on her childhood friend Kio.
- Clingy Jealous Girl: She uses a lot of the spy equipment she got from Jack to listen in on Kio. Leads to the destruction of many pencils and pens.
- Girl Next Door: Manami lived next door to Kio's house before she moved in with him after Kio's house was converted into the Catian Embassy.
- Groin Attack: She kicks Kio in the crotch quite a few times whenever he does something perverted.
- Gun Nut: Harbors Perverse Sexual Lust for a replica Chiappa Rhino .357 magnum.
- Heroic BSoD: She goes through a brief one after realizing that she was responsible for Kio being no longer interested in her.
- I Want My Beloved to Be Happy: She loves Kio, but tries to let Aoi be with him so they can be happy together.
- Literally Loving Thy Neighbor: She's Kio's next door neighbor and she has a crush on him.
- Matchmaker Crush: Encourages Aoi to go for Kio when she learns Aoi has feelings for him, despite her own feelings for him.
- My God, What Have I Done?: After realizing that Kio returned her affections until he overheard her phone conversations and thought she had a boyfriend, she has an emotional breakdown, realizing that it's all her fault that he's no longer interested in her.
- One of the Boys: Manami said that when they were young, Kio was shy around women and she was able to get along with him due to her unfeminine personality.
- Patient Childhood Love Interest: She's Kio's childhood friend, lives next door from him and very obviously loves him, but is reluctant to act on her feelings and would prefer Aoi to have him.
- Pervert Revenge Mode: She can skirt the line between this and Unprovoked Pervert Payback when Kio sees her in unfortunate positions. Really, beating the guy up for walking into his own living room? Or coming running to help you after hearing gunfire in a public street?
- Reckless Gun Usage: Manami displays face-palmingly poor trigger discipline in episode 6, waving a revolver in Kio's face with her finger on the trigger. The gun had just been emptied, but that's no excuse: and she only gets worse later, when she loads the revolver and waves it around in a fast-food joint, once slamming it down on the table while pointed at Aoi. It was quite justified that even though Manami is a gun nut, it was shown that she barely know how to handle guns. And seemingly Kio is better at marksmanship than she is.
- Tsundere: She's Kio's designated pummeler, and also one of his love interests. Unusual for a Type A (harsh), she has no problem admitting that she likes Kio and thinks of him as a close friend, her tsundere tendencies are exclusively based on her romantic feelings.
- Voiced by: Kikuko Inoue (JP), Anastasia Munoz (EN, credited as Staci Moon)
- The Captain: She is the leader of the Catian Starship.
- Cat Girl: She has cat ears and a tail, just like all of the Catians
- Shipper on Deck: For Eris and Kio, though her methods are simply to arrange opportunities for them to spend time together, such as having Eris attend school with Kio, to give their relationship the opportunity to grow rather than any more forceful measures.
- You Gotta Have Blue Hair: Purple
- Voiced by: Aki Toyosaki (JP), Lara Woodhull (EN)
- A-Cup Angst: She notes how swimsuits suit her superior officer's generous figures, as opposed to her.
- You Gotta Have Blue Hair: She has light blue hair.
- Absurdly Youthful Mother: While she looks like a preteen girl, the Light Novels reveal that she has three children of her own.
- Cat Girl: Being a Catian, it's to be expected.
- Older Than She Looks: She looks like a twelve-year-old, but she's old enough to have been Childhood Friends with Captain Kuune.
- Petite Pride: Chaika is fine with her flat chest, unlike Melwin who . . . isn't.
- Shameless Fanservice Girl: She seems to enjoy being naked or in revealing clothing like swimsuits and unlike Eris actually understands what a nudity taboo is.
- Voiced by: Naomi Shindo (JP), Aleshia Force (EN)
- The Comically Serious: She's extremely clinical and open about sex even by Catian standards, which means that she can react to and even participate in the sex comedy around her with a completely straight face.
- The Medic: She can identify health issues other Catians, such as when Eris is in mating season, and can heal them when it's necessary.
- Oral Fixation: She's almost always got a lollypop stick in her mouth.
- Shipper on Deck: A fairly aggressive Kio/Eris fan, explaining to Kio that Eris has chosen him as her mate for her first season and shooting down his objections.
- The Spock: She's always calm and fairly logical in most situations.
A Dogisian in charge of the underground relations between her home planet and governments through Earth. After knowing about the arrival of Catians on the planet, she devises schemes to prevent establishment of official diplomatic relations between them, including trying to eliminate Eris and her friends.
- Big Bad: The main antagonist of the series.
- The Chessmaster: She plots to ruin diplomatic relationships between Catia and Earth.
(light novels only) Jens' younger sister and Nirumea's most important staff officer. She's a brilliant analyst whose "active chart system" provides accurate predictions for future operations.
(light novels only) A warrant officer, superior to Ryunnu and (formerly) Jens. Having a senator within the Barunmuu world government as her father she had become spoiled and manupulative to obtain what ever she wants.
- Voiced by: Hironori Kondo (JP), Jason Douglas (EN)
Jens's personal dog-like assist-a-roid.
- Servile Snarker: He's Jens robot mook, but he laughs at her every time something fails to go her way.
The first Catian Assist-a-roid.
- Badass Automaton: Shown to be immune to the Dogisian Assist-a-roid disabling gas.
- Expy: of a certain movie director
Chiba and Kin
- Driven to Suicide: Just like the manual, when they failed to perform something, their default programming make them attempt a seppuku.
- Expy: of Chow Yun Fat
Other Catian Assist-a-roids, there are 18 of them brought by Eris to Kio's house.
- You Are Number 6: Incidentally, Number Six is the one seen more often, second being the two Number 17.
- Really 700 Years Old: She is an immortal catgirl sage created hundreds of years ago on Earth with magic.
- Serious Business: Make fun of Captain Future in her presence at your own peril.
- Wizards from Outer Space: She practices plain old Onmyōdō, and is otherwise a regular immortal wizard in a sci-fi series.
- Voiced by: Yukiko Monden (JP), Jamie Marchi (EN)
Despite the name, JACK is actually a woman. Her real name is: Janis Alectos Carotenas Karinato. She works for the CIA and is acting supervisor of Manami. She has noticeably long blond hair, is barely dressed and is often seen eating fast food, appearing to the stereotype of American women.
- Cool Car: She drives a Chevrolet Corvette Stingray
- Gender-Blender Name: Jack is a name generally given to men.
- Voiced by: Hiromi Hirata (JP), Martha Harms (EN)
Kio's teacher and leader of Beautiful Contact Japan Sect. Due to the fact Elis doesn't represent the stereotypical alien (tentacles, green skin, etc), she firmly believes that Eris, despite the obvious, is not really an alien.
- Reality Is Unrealistic: She believes this in this strongly, and as a result, feels that Eris isn't a true alien. In one episode, when Eris was trying to help out with the sci-fi film Kio's club wanted to shoot, everything they shot didn't look very realistic, which Ms. Itokazu was quick to point out. Not that anyone was paying attention to her though.
- Crazy-Prepared: He usually seems to have a lot of things handy when the situation calls for it, such as a flashbang grenade when people were trying to attack Kio and Eris, and when Manami and Aoi needed a boat to rescue Kio and Eris, he happened to have one handy when his director coincidentally also needed it for his action movie.
- Reasonable Authority Figure: He doesn't seem too concerned with Kio living with Eris, and doesn't meddle in his nephew's affairs as long as everyone's okay.
Antonia Lirimonie Norfedras Papanorgas Arecroteles Cnorses Morfenoss is a wealthy 12 year old, leader of the Underside of Kitten Paw cult and rarely seen without wearing a pair of cat ears. She grows attached to Kio in the last episode due to him becoming a cat boy.
- Bi the Way: It's fairly clear that she's hot for Eris, but in the last episode, when Kio becomes a catboy, she shows attraction to him too, indicating that she's likely just cat-sexual.
- Fiction 500: The princess knows how to mobilize her money.Antonia: It's shopping time! I want a rocket! I want it now!
- Late for School: when she transfers to Kio's school, she (and her two bodyguards) arrive with a piece of bread in her mouth because she thought it was a Japanese custom for transfer students due to the manga she'd read.
- Lonely Rich Kid: While she has vast wealth and a lot of followers and maids, until she met Kio and Eris, she had no true friends.
- Overly Long Name: She has a very long name, given her wealth and leader of a cult.
- Voiced by: Akeno Watanabe (JP), Clarine Harp (EN)
- Cuteness Proximity: She is very fond of cats or anything that resembles a cat in general when she is within a 100-meter radius around them. So much so, that she takes an interest in one of Eris's assist-a-roids when Manami and Aoi infiltrate Antonia's ship.
- Eyepatch of Power: She wears an eyepatch over her right eye.
- Eye Scream: Sometime before the series, she lost her right eye and had an eyepatch to cover it.
- Voiced by: Sayori Ishizuka (JP), Kristi Kang (EN)
- Rapunzel Hair: She has long hair that reaches to her thighs.
- Scars Are Forever: She has a scar on her lower left cheek.
Alicia Maria Yorkshire
AKA Black Amaryllis, an agent working for the British SIS. Comes from a former British aristocrat family at the age of 16.Born with a heart defect she had gone through a heart reconfiguration surgery that gave her super human abilities.