Follows three sisters, Haruka, Kana, and Chiaki in their lives at home and school. It's a funny series that depicts how these characters interact with each other and their classmates. It's a story about ordinary girls and their ordinary adventures told in an extraordinary manner.
The three Minami sisters and some of their friends are introduced.
Kana decides to help her sister become the Great Bancho once more by making the Kana army, but Chiaki on the other hand couldn't help because she considered her friends useless. In the end of the episode they find out Haruka was just refusing a phone call to become class rep.
During a routine garbage disposal trip, Haruka encounters a boy of Chiaki's age named Fuyuki who is warmly praised by his neighbors for his willingness to freely volunteer his assistance. It is during this encounter that Fuyuki's participation in the weekend neighborhood clean-up is mentioned. Kana's reluctance to take part prompts Haruka to force her and Chiaki to also participate. Later on, Kana summons a few of her classmates, as well as Chiaki's friends to lighten the workload. During the actual clean-up event, it becomes apparent that the work crew Kana assembled was so that Kana could watch while everybody else does all the work.
Chiaki's classmates invite themselves to the Minami home for a group homework session and sleepover. Kana declares it a 'pyjama festival' and puts herself in charge of hospitality, to Chiaki's annoyance. To feed all her guests, Haruka prepares a family-style nabe meal, and she invites Fujioka and Makoto to dinner. Everyone has a good time, but no-one gets much homework done.
The Minami sisters, Makoto, Touma, Fujioka, and Takeru go on a hot spring trip for New Years.
It's Valentines Day and the Minami sisters are making chocolates to give out. Kana tries to eat Fujioka's chocolates, but he tries to keep them a secret from her, hoping that Kana will give him chocolate.
The power goes out and the Minami sisters invite Fuyuki over.
Kana and Chiaki break a glass rabbit necklace that Haruka had bought. Worried that the rabbit was a gift to Haruka that she treasures, both Kana and Chiaki try to repair the rabbit. After the repairs go badly, Kana tries to get Fujioka, Keiko, and Yoshino to look for another to replace the broken rabbit. In the end, Haruka discovers the truth.
A local shop owner gives Haruka tickets to a new indoor pool. We learn that Chiaki doesn't know how to swim and doesn't want the others to find out. Later, Kana tries to teach Chiaki how to swim and help Chiaki meet her goal to swim 100 meters. Haruka sleeps the entire time, trying to ignore her sisters, until her highschool friends throw her into the pool.
The Minami sisters' daily school life is shown. Some of their classmates are introduced as well.
Kana teaches Chiaki's friends about how to deal with a suspicious man. Meanwhile, Haruka's legendary past in her junior high school is revealed.
Hosaka tries to get close to Haruka by making impressive bentos for her.
The Minami family and the neighboring Minami family are having their own Christmas eve, while Hosaka is preparing a soba bowl to impress Haruka.
The Minami sisters' daily life at home is shown.
Toma, a tomboy from another Minami family, is introduced while Makoto is still pretending to be a girl in front of Haruka.
During a lazy afternoon, Kana decides to help herself to some oranges while Touma and Chiaki read at the kotatsu before getting the idea to snack on an orange. It is not long before Makoto and Uchida learn the root cause: Kana delivering a preemptory »Hands off my oranges; go get your own!!!« karate chop to both Chiaki and Touma. Another arc has everybody galvanized by the Yuletime ambiance: Chiaki synthesizing a huge stocking and leaving it to chance what present she receives, Touma learning to appreciate »useless/annoying« family rituals, and Hosaka acquiring a part-time job as a cake salesman dressed in a Santa Claus suit even though he does not encounter Haruka by that avenue as per his daydream. Haruka hosts a Yuletime banquet at her house.
Touma's ecstasy during the homebound commute is quickly extinguished by Natsuki helping himself to the snack consecrated for that purpose. Thereafter, Touma's sudden arrival on Chiaki's doorstep gives way to the revelation that Touma has an ongoing passive-aggressive dynamic with her brothers and paints a dysphoric snapshot of Touma's family. The next arc details how the Minami sisters deal with an abundance of apples. The arc concludes with the Minami brothers prosecuting protracted and complex computations regarding the utilization of the apple Touma brought back with her. The arc that follows thereafter details Haruka conferring culinary counsel upon Natsuki while Kana and Chiaki discuss Haruka and Natsuki first as individuals and then as a romantic couple. Chiaki dismisses the prospect before directing Kana to finish the curry Haruka is making. Unfortunately, the culinary protocols for both Haruka's curry and Natsuki's cookies get interchanged with dysphoric consequences. The final arc is related to the first and details the conflagration of Touma confronting Natsuki who repels his brothers' attempts to come to their sister's aid. In an attempt to guide her through guarding against this kind of misunderstanding, Kana demonstrates to Touma a form of Japanese script that looks a lot like arithmetic.
A euphoric beach outing having the dysphoric prologue of Kana being carsick is reflected upon warmly by Uchida and Yoshino who have taken the whole experience in stride. Yoshino remarks that Chiaki has become attached to Fujioka as an elder sibling in much the same way that Kana has with Uchida and her. Chiaki's exhortation for the whereabouts of her teddy bear disrupts the reminiscence; fortunately, Fujioka brings it back and Kana successfully obfuscates her role. Maki tempers her disdain for her summer homework by successfully wielding Fujioka's computations as her plaything until Kana and Chiaki extinguish her machinations. The next arc features Uchida having a near-complete computation crash as she struggles to complete her summer homework without Chiaki's counsel as the penance for abusing Chiaki's goodwill. Fortunately, Chiaki is not heartless; she eventually relents after seeing Uchida and Makoto's demonstration of interdependence being a two-way street. The final arc features Kana's attempts to forestall the approaching autumn backfiring upon her as Chiaki, galvanized by all the pranks Kana played on her, retaliates by eating Kana's dinner in addition to her own.
Fujioka approaching Kana with a book for Chiaki and Riko computing the approach thereof gives way to another girl named Hiroko taking notes of the whole scenario from afar before conscripting Riko into an exercise to build up the courage necessary for a confession that flounders. The next arc details Kana conducting her volition of a study session at her home with Keiko and Fujioka that Riko decides to capitalize upon. The study session's academic success contrasts with the fact that Riko has not once confessed her feelings seeming content to enjoy the ambiance of proximity to Fujioka. Fujioka, Riko, and Keiko nearly have a computation crash when they go into the bathroom to find the bathtub covered in order to keep the water hot and decide to shower instead. The arc the follows thereafter details the epilogue of a recent test in which Riko, Fujioka, and Kana's test scores are close to Keiko's perfect score. The final arc begins with a conversation between Makoto and Touma over being given chocolates as a Valentine's Day joke prompting Kana deciding to play Othello after telling Chiaki that she needs to practice celebrating Valentine's Day to gain the experience.
Chiaki lashing out at Uchida, Kana, and Maki due to their boisterous laughter rousing her from a nap on a warm spring day gives way Kana first sending in Uchida and Maki to fight this battle for her before doing her own dirty work only to have it end in a stalemate. The next arc features Makoto and Uchida taking an afternoon nap with Kana when Maki pays the trio a visit with the request that Kana gaze upon her sleeping face while recalling a dysphoric middle school memory, especially after Kana reads Maki and Uchida sleeping as the perfect opportunity to draw on their faces as a prank. The arc thereafter features Haruka and Atsuko looking at pictures from their middle school days. The arc that ensues has Chiaki sewing on a wayward button while Kana detects Haruka's school uniform carelessly strewn about before remarking of the seasonal uniform transition. While modifying a shirt of Kana's, Chiaki accidentally slices Haruka's fuku skirt. Knowing that Haruka will be very angry with them when she detects the damage, Kana and Chiaki attempt some desperate and frenzied repairs to buy time for computing their next move. Unfortunately, things coming unraveled when Maki detects the telltale thread put both Kana and Chiaki in scalding hot water with Haruka. The final arc features Kana blowing up at Chiaki for insulting her once too often before deciding to resolve her fears of Chiaki becoming a delinquent by being a nice older sister. Unfortunately, all Kana accomplishes is to greatly unsettle Chiaki and frighten her into co-sleeping with Haruka.