Monsters—they're real, and they want to date us! Three years ago, the world learned that harpies, centaurs, catgirls, and all manners of fabulous creatures are not merely fiction; they are flesh and blood—not to mention scale, feather, horn, and fang. Thanks to the "Cultural Exchange Between Species Act," these once-mythical creatures have assimilated into society, or at least, they're trying.
When a hapless human named Kurusu Kimihito is inducted as a "volunteer" into the government exchange program, his world is turned upside down. A snake-like lamia named Miia comes to live with him, and it is Kurusu's job to take care of her and make sure she integrates into his everyday life. Unfortunately for Kurusu, Miia is undeniably sexy, and the law against interspecies breeding is very strict. Even worse, when a ravishing centaur girl and a flirtatious harpy move in, what's a full-blooded young man with raging hormones to do?!
Kimihito wakes up to find Miia crushing him in her sleep. After escaping, he draws a bath for her to warm up and goes to make breakfast. In the kitchen he is surprised by Smith, who has come to make sure he isn't engaging in any prohibited activities with Miia, such as sex. After Smith leaves, Miia tries to seduce him, only to accidentally dislocate his shoulder. The two go on a field trip, including a visit to an all-species lingerie shop. Afterwards, they run into a racist couple who harass Miia, and Kimihito has to jump in the way when she tries to strike them with her tail, to keep her from breaking the law. Trying to escape from a curious crowd, they hide in a love hotel, where they are ambushed by the Interspecies Exchange Security Squad. However, Smith recognizes them and fixes the situation. Leaving the hotel, they encounter the couple, and when they begin harassing Miia again Kimihito punches them. At home, Miia resumes her advances on Kimihito, only for them to be interrupted by Smith.
Kimihito is kidnapped by Papi, who brings him to a park, where they buy ice cream. Papi then takes a bath in a public fountain, where Miia finds them. With various mishaps, the three work together to save a girl who was stuck in a tree. When a policeman arrives, Kimihito claims to be Papi's host family to keep her from being deported. The officer is skeptical, but Smith arrives with Papi's papers just in time, and tells Kimihito that she was on her way to make the harpy live with him. While out grocery shopping, Kimihito collides with Centorea. She becomes convinced that Kimihito is her soulmate. Encountering a purse-snatcher, the two pursue him. They eventually catch him, despite various embarrassing accidents. When the thief tries to attack Centorea with her dropped sword, Kimihito leaps in front of her and takes the blow, but survives due to the sword being a fake. Later, Smith explains that Kimihito riding Centorea could be viewed as akin to rape, since only a centaur's chosen master may ride them. Centorea chooses him as her master, resulting in her joining his household.
When Papi tries to seduce Kimihito during their bath, Centorea rescues him and they flee to the park where they share a tender moment. They are soon followed and interrupted by Miia and Papi, and the three begin fighting for Kimihito's affection. Smith arrives with a tranquilizer gun to stop them, but accidentally shoots Kimihito instead. When he wakes up at home, the three are apologetic for the harm they have caused him, but he dismisses their worries. Smith then announces that there has been a change to the Interspecies Exchange Bill, and she wants him to marry one of the girls as a test case. That night, Miia arrives in his room and tries to seduce him, only to be interrupted by Papi, who crashes through the window. Centorea arrives and explains that the full moon is to blame their abnormal behavior; however, it soon becomes clear that she is also affected.
Miia opens the pot on the stove and is attacked by a slime. Centorea explains that slimes are one of many species as yet unrecognized by human society; the slime then attacks again, and when Centorea's sword has no effect, both her and Kimihito end up covered in slime. When he goes to take a bath, she joins him after being unable to get clean. She conjectures that the slime was attacking them to get water; it then attacks them again in the bath. When Centorea falls and is knocked unconscious, the slime takes the form of a woman and begins imitating his washing of Cerea; due to her body being liquid, however, she almost drowns him before he escapes by diluting her in the tub. They debate what to do with her, and Papi reveals that she has named her Suu. The girls point out that she is likely an illegal immigrant; Papi overhears this and flees with Suu, thinking they mean to turn her in. When Kimihito catches up with them, they are apprehended by a group of children who often play with Papi. When one of the children is almost hit by a truck driven by the racist couple from the first episode, Suu saves her but falls off a bridge. Luckily, Kimihito gets under her with the crashed truck before she falls in the water. After that, he decides to let her stay at his house. They go home, only to find Smith there.
A construction crew from the Interspecies Exchange Security Squad arrives while the girls are making a plan to hide Suu from Smith. The girls leave with Suu until the construction is over, only to realize that they have left Kimihito behind. They are forced to hide when pursued by security forces. All three of the girls somehow get wet, causing them to be assaulted by a dehydrated Suu. Meanwhile, Kimihito is searching for them. He is hit by a girl in a runaway wheelchair, who introduces herself as Mero. When they arrive at the park, Mero is almost assaulted by Suu, but Kimihito catches her in a plastic bag. Arriving home, they thank Smith for building a room for Suu; she reveals, however, that the room is not for Suu, but for Mero, who is revealed to be a mermaid. Miia becomes jealous when her accidentally breaking Mero's wheelchair results in Kimihito having to carry the mermaid around the house. She attempts to enlist Centorea and Papi's help in foiling the mermaid. When Kimihito knocks Mero into the pool to save her from a once-again dehydrated Suu, Miia thinks he is making a romantic advance and dives in after them, almost drowning when the cold water makes her sluggish. Later, as Miia and Mero take a bath together, the mermaid reveals that she has no intention of attempting to woo Kimihito away from Miia; all mermaids want to experience a tragic love similar to "The Little Mermaid". Centorea and Papi overhear this and believe that the two are plotting against them.
Miia trains to become Kimihito's bride by throwing herself into cooking. However, she seems absent minded and burns both of her hands. She is out of sorts because she is shedding. She cries that she is useless and can't even shed by herself, but Kimihito cheers her up and offers to help her shed.
A standoff involving a high school girl held hostage takes place at a doujin shop. The Orc Pioneer Federation demands that "orc x female knight" adult comics be made mainstream. Smith's "MON" arrives at the scene. They are a special squad assembled to handle crimes committed by non-human species!
Rachnera settles in as a member of the Kurusu household; however, Miia and Cerea, who don't trust her, are not so enthusiastic about this. Cerea begins to stick very close to Kimihito, protecting him from potentially embarrassing situations created by Rachnera. When Rachnera tries to seduce Kimihito in his bedroom, Cerea rescues him and flees with him into the city streets. The male from The Couple and his gang begin harassing Kimihito and Cerea, but Rachnera makes a timely appearance and rescues the two. She then comes to an understanding with Cerea, and Cerea realizes that Rachnera can be trusted. Later, Kimihito comes down with a bad cold and Ms. Smith immediately puts him in quarantine in his bedroom and orders the other girls to keep away from him, fearing a possible pandemic. She states that she will care for Kimihito, but almost immediately conks out.
The girls are shocked when it appears that Kimihito is going on a date with Ms. Smith. Miia, Papi, Cerea, Mero and Suu immediately begin following them, first to a maid cafe (where Mero disguises herself as one of the maids, using Suu as a uniform), then to an arcade (where Papi is disguised as a cosplayer), then to an ice cream truck (where Miia and Cerea impersonate servers), but they fail each time. Finally, Miia follows Kimihito and Ms. Smith to a love hotel, where she meets up with Rachnera (who has been trailing them all along). Rachnera tries to sneak into Ms. Smith and Kimihito's room, but is hindered by Miia, who causes them to be grabbed by the MON Squad. Ms. Smith explains that Kimihito had received a threatening letter from someone named "D," and their "date" was actually a ploy to lure the culprit out.
Kimihito's second "date" involves an outdoor barbecue (in a wooded area where industrial nutrient waste was once dumped) with Papi and Suu (with Zombina, who is supposed to be shadowing them, freeloading on the cooking meat!). However, the barbecue is interrupted by a giant tree kaiju that seems to know Papi and grabs both her and Kimihito. Papi recognizes her as Kii, a dryad she had once rescued (but completely forgotten about), but Kii (who has been poisoned by the illegally dumped waste) is on a rampage with a grudge against all humans and stomps Zombina into the ground. Suu (who fell into the industrial waste) grows to Godzilla-size and battles Kii to save Kimihito and Papi; she tells them that the only way to stop Kii may be to extract the waste from her body ... which they are forced to do using a very lewd/embarrassing (but for Kii enjoyable!) method. With Kii calmed and restored to her normal size (and cleared from being the mysterious "D" because she can't write), Ms. Smith offers her a new host family, but she decides to remain in the forest, as long as Papi and Suu can visit her. The third "date" is with Cerea, who is going all out to protect Kimihito (including wearing full armor!). Manako, the MON member shadowing this "date" and already completely flustered by Cerea's intensity, is completely blindsided by Lilith, a devil, who looks like a child but is actually an adult and enjoys pulling pranks on people; Lilith then turns her hypnotic tricks on Cerea, who because of earlier incidents is feeling inadequate as Kimihito's "servant", but the prank is interrupted by a very large and angry wild boar that attacks her. Kimihito manages to distract it and Cerea subdues it, and Kimihito reassures Cerea that he trusts her and has done so from the beginning. Cerea's confidence is restored and she is put in charge of salad-making, but Lilith, who tried her tricks on Rachnera (who had been secretly keeping an eye on Kimihito and Cerea), is caught and severely "pun
Frustrated because of their repeated failure to uncover the mysterious "D", who has sent a second and more threatening letter, the MON members (minus Doppel, who isn't interested) decide to take matters into their own hands and have Kimihito date each and ALL of them in one day! First, Tionishia nearly kills Kimihito by dragging him (literally!) off to different shops, including a dress shop where even the largest size proves too small for her, but Kimihito's revealing that he can expertly alter normal clothing to fit liminals wins her over. Next, Zombina drags Kimihito off to a zombie film; later, when her hand comes off and he uses his sewing skills to reattach it, she is impressed (as well as by his seeing her as a girl and a person rather than a "monster") but in order to tease him deliberately detaches a breast and gets him to sew it back on as well! The last "date" is with a very self-conscious Manako, who becomes flustered by his being able to look her straight in the eye. The "date" is interrupted by Manako spotting a shadowy figure following them, and all three MON girls team up to apprehend the stalker, who is indeed "D" but revealed to be Doppel, who sent the first letter as a joke ... but not the second, as Kimihito finds out when a scythe is pressed against his throat by a mysterious girl with purple skin and dressed in black! Later that evening, the girls are shocked when Kimihito brings home a headless girl, totally freaking Miia out! Kimihito, Cerea, Papi, Mero and a very reluctant Miia search the nearby park where the head rolled into; the head is eventually located and actually talks to Kimihito, admitting that she sent the second letter and asking him to restore her to her body! The conversation is interrupted by the jumpy police officer, who totally freaks out upon seeing Kimihito holding the head! Thanks to some unexpected and unintentional help from Papi, the gang gets away and returns home with the head. Once she and her head are restored to e
To prevent the dullahan from collecting Kimihito's soul, the girls decide to take him away from her as far as possible, but their attempts only cause more injures to him as usual, until Rachnera appears with the dullahan, claiming that if she is really a reaper of souls, there is nothing they can do to prevent his death. When Miia decides to die along with Kimihito, claiming that she cannot bear losing him, Kimihito decides to stop running away and face his imminent death as the dullahan predicted, but to everybody's surprise, nothing happens. Back at home, Kimihito and the girls discover from Ms. Smith that her name is Lala, and she is no reaper of souls at all, having ran away from several host families where she previously lived, and lets her live with Kimihito and the others by her request. When questioned about how he saw through Lala's lies, Kimihito answers that he just realized that she has a late case of eighth grade syndrome, and when questioned if he had such thing when he was younger, he denies it, but a quick flashback shows that he did. Some time later, Kimihito realizes that he is at the end of his savings and there is no more food in the house after Miia's attempts to cook ended up in a total disaster. He then sets up for groceries with Cerea, Papi, Mero and Suu, and the monster girls' sympathy with the local vendors earn them some merchandise with a special discount. To obtain some extra vegetables, Kimihito and Suu pay a visit to Kii, who guides them to an area with several plants, and Kimihito learns that Suu has the capacity to diferentiate the edible ones from the poisonous ones by tasting them. On the way back home, Kimihito is attacked by Draco, but Suu defends him with the poison she stored inside her body during the plant tasting. Once returning, Kimihito prepares dinner for the girls, when Ms. Smith and the girls from MON suddenly appear to dine with them as well exausting all of the food's house supply once again, but Ms. Smith explains th