Yukinari Sasaki the series main character. Because of his small stature and generally meek disposition, Yukinari has been bullied by girls his entire life and therefore suffers an allergic reaction that causes him to break out in hives whenever he comes into contact with a woman. One day, he is knocked into his bathtub and is transported to the alien world of Seiren, a planet where men comprise less than 10% of the population. Upon arriving in Seiren, Yukinari meets a young girl named Miharu who for some reason does not cause him to break out on contact. Yukinari has a bad habit of being in the wrong place at the wrong time. This, along with other 'close encounters', gets him kicked, punched, and otherwise beaten up by Kirie. He lives alone in the anime. At the beginning of the manga he lives with his mother and works to keep Miharu's presence secret. Before the end of the first volume his mother leaves to take care of his father, who has suffered a physical collapse while on a business trip, and is not seen again.
Voiced by: Mamiko Noto (Japanese), Yuri Lowenthal (English)

Miharu Sena Kanaka a pink haired resident of Seiren who pulled Yukinari into her world and later followed him back to Earth to live with him. She has a mark shaped like three dots in a triangular arrangement on her forehead which provides her with several powers, such as the ability to transfer between Seiren and Earth and the power to create explosions whenever she's under emotional distress. She is also the only woman that can touch Yukinari without triggering his allergy. Miharu has an outrageous appetite and an impossibly rapid metabolism. She spends most of the series questioning her friends whether something is edible or not (like butterflies) and her continuous misunderstandings about earth (IE-believing that April Fools Day means that everyone on Earth lies for one day) is the title's primary source of humor. Despite this, she has a heart of gold, an explorers' fascination with earth and a genuinely open affection for Yukinari. She is an innocent girl who does not lose her temper even when made the target of Fukuyama's lecherous actions; unless in the process he eats or otherwise ruins whatever she happens to be eating at the time.
Voiced by: Ayako Kawasumi (Japanese), Michelle Ruff (English)

Kirie Kojima Yukinari's neighbor and classmate who takes care of him from time to time. She's especially well-endowed which makes her a natural target for Kazuharu Fukuyama's perverted actions. However, due to her physical aptitude and martial-art abilities, she always manages to turn the tables on him. She also sometimes punishes Yukinari for his 'perverted' actions, although they are accidental on Yukinari's part. Kirie accidentally sends Yukinari to his first arrival into Seiren when she slugs him for unintentionally peeping on her when her shower wasn't working correctly and used Yukinari's instead, which lead him to fall into the bathtub. Despite their somewhat turbulent relationship, it's occasionally hinted that she does actually possess deeper feelings for Yukinari. Because of her strong character, Kirie seems to attract a large number of admirers among the boys in her high school. In the anime she also attracts female admirers; specifically Kosame and Ms. Hijiri; much to her chagrin although in the manga Kirie was accosted by an alternate version of Lisa when she entered a parallel world through an enchanted mirror in Fukuyama's house. A running joke throughout the series is Kirie's complete lack of cooking skills which result in the creation of food that's not only inedible but health hazardous as well. In fact, Fukuyama once ate a bento lunch prepared by her and fell ill. Kirie suffers an overwhelming fear of ghosts and the paranormal and despite her tomboyish character enjoys collecting dolls.
Voiced by: Chiwa Saito (Japanese), Stephanie Sheh (English, credited as Lulu Chiang)

Kazuharu Fukuyama a classmate of Yukinari and Kirie and the series primary antagonist. Fukuyama is rich, powerful, and perverted and while he often chases girls and picks on Yukinari (who he nicknames "chibi-nari", or "puny-nari" in the English dub) he does show a serious, caring side in critical situations. He is a severe androphobe to the point that he's developed an allergy that causes him to break out with a rash whenever he comes into contact with another male. Extremely stealthful, he has the ability to suddenly appear without the others noticing until he announces his presence whereupon he either gropes or strips the girls of their clothing which always results in him receiving a severe beating from Kirie. Despite his own lecherous behaviour, Fukuyama is highly protective of his younger sister Lisa and strongly objects to her affections for Yukinari.
Voiced by: Ryotaro Okiayu (Japanese), Liam O'Brien (English)

Lisa Fukuyama, Fukuyama's younger sister. Lisa is a master of black magic which has caused more than a few problems throughout the series (IE-infesting her family's mansion with ghosts, summoning a giant octopus in the school swimming pool, causing an explosion within a shopping center). Lisa is constantly accompanied by Hayate and Kosame who cater to her every whim such as gathering intelligence or even kidnapping. She has an infatuation with Yukinari, much to Kirie's dismay, and often employs her magic to try to get closer to him with predictably disastrous results. Although she dislikes Miharu at times, she is very fond of Ebi who reminds her of the pet cat she owned when she was a little girl. In the anime, Ebi's girl form reminds her of the beloved doll she used to spend her days with, which she was reunited with later on in the series.
Voiced by: Yuki Matsuoka (Japanese), Hunter MacKenzie Austin (English)

Koyomi Hare Nanaka a resident of Seiren who suffers a paralyzing fear of men. Her phobia is only made worse by being one of Fukuyama's favorite targets which results in her keeping a diary of the many times he's accosted her in the manga. Originally sent to Earth on a mission from the Space Travel Agency to 'retrieve' Miharu, she later moves into Yukinari's house on a prolonged mission to find Maharu, Miharu's sister, a groom. Of course, her male phobia makes the act of even talking to a man nearly impossible. In the anime, Koyomi is also searching for her long-lost father, a native of Earth, whom she later reunites with at the series' end. Koyomi's favorite pastime is reading and she has a natural talent for table tennis. In the anime she's even won the Seiren tournament five years in a row. Koyomi's mother possessed a Seikon mark like Miharu and Koyomi herself possesses a dormant form of Seikon which allowed her to create a portal to Seiren after Miharu was kidnapped in the anime. Koyomi in the anime also adopts a large python as a pet after being tricked into wearing it over herself during Fukuyama's Cosplay Mahjong game, which is ironic considering her fear of men and snakes being a phalic symbol.
Voiced by: Masayo Kurata (Japanese), Carrie Savage (English)

Tomoka Lana Jude a resident of Seiren who was sent to aide Koyomi in finding Maharu a groom after Koyomi's less than productive efforts. Although a child, Tomoka deeply resents being treated as one and insists that she's as mature as anyone else, despite frequent actions by her which prove otherwise. Unlike the other female characters, she gets along fairly well with Fukuyama (presumably because she's too young for him to have any sexual interest in) who she refers to as "big-brother" and the two occasionally partner up to obtain some mutual objective of theirs. In the anime, Tomoka frequently uses Ebi as a makeshift club for hitting almost anything and anyone. Tomoka can also use transformation magic, and in the anime becomes friends with Lisa after conceding defeat in a magical duel. She is also obsessed with Poyon, her favorite TV show character. Because she's a child, Tomoka is able to have contact with Yukinari without triggering his female allergy. She also looks up to Kirie as a "big-sister" (onee-chan in the original dub). For example, she follows Kirie's example of drop-kicking Fukuyama right in the face. In the manga, Tomoka is later revealed to be a genius capable of instantly answering a complex math equation from a college entrance exam.
Voiced by: Ayaka Saito (Japanese), J-Ray (English)

Ebi a rare and magical creature from Seiren; Ebi in the manga was accidentally summoned by Miharu during a bath whereas in the anime she was accidentally brought to earth in Tomoka's luggage. In both version, Miharu adopts her as a pet although in the anime she originally wondered if Ebi would taste good. She resembles a plump miniature seal with the face of a cat and a pair of large bobbing antenna, which causes Miharu to claim she resembles a shrimp and is where her name came from (ebi being the Japanese word for shrimp). Ebi in the anime suffers a great deal of torment at the hands of Tomoka who uses her as a flail, fishing bait, a handball, or to display Tomoka's magical knowledge by turning Ebi into a small green-haired girl. Although in the manga Tomoka only did it briefly as Yukinari and Kirie showed more attention to the transformed Ebi than her. Ebi is surprisingly intelligent and during a Mahjong match in the anime, she thought through the entire play in her mind. Unfortunately, Tomoka was a novice and Ebi couldn't speak human language, rendering her plan fruitless. Ebi in the anime is also able to shoot a powerful beam attack (called the E-beam by Tomoka) from her mouth.
Voiced by: Tomoko Kaneda/Fumihiko Tachiki (Japanese)

Minor characters

Maharu Sena Kanaka, Miharu's well-endowed older sister. She is very determined and won't hesitate to use to violence to get her way. Although initially jealous of Miharu's relationship with Yukinari she later gave her blessing for them to be together. Much to Yukinari's dismay that does not stop her from flirting and fondling him whenever she gets a chance. Due to Seiren's low male population and the fact that she's inching dangerously close to 30, Maharu assigns both Koyomi and Tomoka to find a man of her own on earth. Though flirtatious, she is, in fact, quite picky by Seiren standards; rejecting Fukuyama immediately upon discovering his perverted nature. In the end of the anime she asks Hayate if he would like to get married, but an answer was not given.
Voiced by: Sayaka Ohara (Japanese), Karen Thompson (English)

Hayate, one of Lisa's attendants. While he only makes a handful of appearances in the manga, Hayate in the anime forms a strong rivalry/friendship with Tomoka and the two occasionally battle one another in friendly duels. Hayate is a very calm, loyal, and serious individual who will go to great lengths for his mistress, Lisa, which usually involves doing some sort of research or private investigating. Tomoka nicknames him "ninja" because of his stealthy ways, only revealing himself when attending to Lisa, or to attack.
Voiced by: Takanori Hoshino (Japanese), Patrick Seitz (English)

Kosame, Lisa's second attendant. She has a much larger role in the anime than the manga where, after a battle with Kirie, she becomes completely infatuated with her. Her obsession is so strong that just being in Kirie's presence is enough to make Kosame either grope or make some other pass at her, which occasionally requires Hayate to hold her back. When not fawning over Kirie, Kosame is as stoic a figure as Hayate and frequently uses her gun to either pry information out of others or to force them into doing her bidding. In the anime she is also a considerably stronger fighter then Kirie.
Voiced by: Nozomi Masu (Japanese), Robin Rhodpa (English)

Mamoru Machida, a classmate of Yukinari's who is obsessed with cleanliness and dons an alter-ego, Lightning Squadron Mamo Ranger, in the pursuit of his passion, although at first glance his 'squadron' consists of only him. Extremely accident prone, he tends to cause more damage than he solves whereupon his deluded sense of reality causes him to blame his "villainous opponents." In the manga, he later drafts the others into the Mamo Rangers who want absolutely nothing to do with it. In the anime, Mamoru becomes an apprentice to Lilica which turns him from a mild annoyance into a serious threat to public safety.
Voiced by: Hiroyuki Yoshino (Japanese), Sam Riegal (English, credited as Sam Regal)

Lilica Stacy, Kazuharu's chief maid. She is even stronger than Kirie, having fought in military operations in Bosnia, Somalia, Chechnya and Afghanistan. Lilica is highly intelligent and is often seen with a laptop, which serves various purposes, such as operating the mechanical devices within the Fukuyama mansion and deploying a surveillance software from a spy satellite orbiting earth. This is how Fukuyama constantly finds Koyomi and the others. In the anime, Lilica took on Mamoru Machida as an apprentice after being impressed by his desire to protect the world from grime and dirt. She is also occasionally hinted to be in love with Fukuyama.
Voiced by: Natsuko Kuwatani (Japanese), Wendy Tomson (English)

Nanae Kuh Haruk, Koyomi and Tomoka's superior in the Space Travel Agency. Nanae is in charge of the missing persons department and assigns agents to find and retrieve residents of Seiren who have accidentally been transported to Earth. At the end of the anime, she helps Maharu contact Yukinari so that the others can rescue Miharu.
Voiced by: Yukiko Iwai (Japanese)

Hijiri Kanata, a very strict teacher at Yukinari's high school. In the anime, she was actually a spy for Yukina whose mission was to observe and eventually kidnap Miharu. Hijiri had been obsessed with Miharu since they were both children and Yukina promised to give Miharu to her in exchange for helping her eliminate all men. After being defeated by Kirie however, Hijiri forgot about Miharu and began to lust after Kirie instead, something that neither Kazuharu nor Kosame took very likely.
Voiced by: Aya Hisakawa (Japanese), Erica Shaffer (English)

Yukina, the ruthless head of Seiren's Space Management Bereau's Special Forces Division, who also has the power of Seikon like Miharu and Koyomi. Because of her slight build and her Seikon mark which completely covers her body, Yukina felt that no man would ever love her and thus developed a condition that causes her to break out in hives upon contact with men, similar to Yukinari and his allergy to women (hence her name being similar to his). Her illness and anti-masculine prejudices are the reason for Seiren's low-male population as Yukina decreed that if she couldn't be loved than no one would. At the end of the series, Yukina has her lieutenant Hijiri kidnap Miharu and bring her back to Seiren so Yukina could steal Miharu's power and use it to eliminate all men in both Earth and Seiren. But after being shown kindness by Yukinari, Yukina returned Miharu and even fell in love with Yukinari since he does not trigger her hives, even though she triggers his. Yukina was made exclusively for the anime series and does not appear in the original manga.
Voiced by: Sakura Nogawa (Japanese), Elise Baughman (English)

The Boss, an anime exclusive character. The Boss is a tall and heavy set man of few words dressed in a Hawaiian shirt and is usually accompanied by a loud-mouthed sidekick in a blue leisure suit. He and his companion cross Yukinari and the other's paths throughout the series but the Boss does not speak until after Miharu is kidnapped whereupon he helps Yukinari realize that the only way to get Miharu back is to fight for her with everything he's got. When his sidekick later asks why he never spoke before, the Boss shrugs and replies that he simply never had anything to say.
Mrs. Sasaki, Yukinari's mother who appears only in the manga. As Yukinari kept Miharu a secret from her, Mrs. Sasake began to fear that the strange occurrences in her house where due to a ghost, but eventually decided not to worry about it since all the "ghost" did was eat all the food. She is not seen past the manga's first volume.