(pasted from wikipedia)
Yotsuba&! is centered on the antics of Yotsuba Koiwai, a five-year-old adopted girl who is energetic, cheerful, curious, strange, and quirky—so strange and quirky, in fact, that even her own father calls her a weirdo. She is also initially ignorant about many things a child her age would be expected to know, among them doorbells, escalators,air conditioners, and even playground swings. This ignorance results in humorous stories where she learns about, and frequently misunderstands, everyday things.
At the start of the series, Yotsuba and her adoptive father, Koiwai, relocate to a new city with the help of Koiwai's best friend, an impressively tall man nicknamed Jumbo. Yotsuba makes a strong impression on the three daughters of the neighboring Ayase family, Asagi, Fuka, and Ena, and many of her misadventures come from interactions with them.
The series has no continuing plot—the focus is Yotsuba's daily voyage of discovery. Significantly, many chapters can be identified as taking place on successive days, which reinforces the sense of that we are following the characters' daily life. The tone can be summarized by the motto, used on chapter title pages and advertising, "Today is always the most enjoyable day" ("Itsu de mo ky? wa, ichiban tanoshii hi").
Kowai Houshold
YotsubaThe protagonist of the story, she is a self-styled six-year-old (she is actually five years old) with a child's wonder towards even the most unremarkable of new discoveries. Her ability to find enjoyment in nearly everything is unparalleled, and her constant enthusiasm is infectious. Before moving to her present house, she lived with her adoptive grandparents, then before that on an island that is, according to her, "to the left." Nothing is known about her parentage other than that Yotsuba was orphaned somewhere outside of Japan and subsequently taken in by Koiwai, and she is sometimes taken for a foreigner by strangers. She herself seems to have no memories of her birth parents, and is confused by the concept of having two sets of grandparents. She is an excellent swimmer, but not as good an artist as she thinks she is.
The name "Yotsuba" (??) can be translated as "four leaves," and is part of the phrase ???????? yotsuba no kur?b? ("four-leaf clover"). In reference to this fact (or perhaps because of it), Yotsuba has four ponytails and green hair.
Mr. Kowai("Dad")Koiwai, given name unknown, is Yotsuba's adoptive father. The circumstances of Yotsuba's adoption are obscure (in chapter 7, he says it happened somewhere overseas), but she treats him as though he were her biological father. He works as a translator, though what languages and materials he translates is unknown to the audience since it does not matter to Yotsuba. He has a loose attitude about things, and always wears a t-shirt and boxer shorts when working at home; he apologizes more than once for being "irresponsible." He seems to frequently become frustrated by impasses in his translations, but when he finishes his work, he is quite happy to spend time having fun with Yotsuba. Regardless of his skills as a parent, it seems that Koiwai is a good father at heart.
Ayase Household
They live next door to the Kowais!
Asagi Ayase(the "pretty one")The eldest of the three Ayase sisters, she is a university student at home for the summer break. According to Yotsuba, she is the "pretty one". Asagi is attractive and physically mature, but enjoys teasing people, especially her mother. If she is aware of Jumbo's crush on her, she has not said anything. She is the best of her family at managing Yotsuba, and her mother claims she was much like Yotsuba when she was young. Asagi's irreverence may have something to do with her mother's teasing her as a child (for example, when Asagi found a four-leaf clover, her mother asked for a five-leaf clover instead, which Asagi could not find).
Fuka Ayase (?? ?? Ayase F?ka)Fuka Ayase(the "un-pretty one")The middle Ayase sister, she is a 16-year old student at a local high school, and the most responsible of the three. According to Yotsuba, she is "the one that wasn't pretty" or "the un-pretty one". Nonetheless, she becomes quite fond of Yotsuba. She finds herself frequently helping out at the Koiwai household, even though she does not intend to and is more flustered by their eccentricities than anyone else. One running joke is that Fuka is terrible at drawing. She also has a penchant for bad puns, and for wearing shirts with odd or interesting graphics (one being an image of Chiyo's "father" from Azumanga Daioh).
Ena AyaseThe youngest Ayase sister, she is a few years older than Yotsuba, but the closest she has to a true peer. Ena is sensible for her age and tries to be responsible by doing things like recycling and limiting her use of air conditioning. She is sometimes flustered by Yotsuba's antics but she also enjoys playing with her younger friend. Her attempts to spare Yotsuba's feelings sometimes lead her to make little white lies, such as praising Yotsuba's childish sketches, with consequences that rebound on herself and Miura.
Ena likes drawing, something at which she is quite skilled, and playing with her teddy bears, either by herself or with Yotsuba. Despite her "girly habits", Ena is remarkably unsqueamish and even enthusiastic about things that would gross out most ten-year-old girls, such as handling large frogs and gutting live fish.
Mrs. Ayase / "Mom" (????? Ayase-ke no Haha / ????? k?-chan)
The mother of the Ayase sisters, who frequently has Yotsuba over as a visitor. Unlike her daughters, she seems to be unfazed by Yotsuba's habit of calling her "Mom". She is frequently angry with Asagi, possibly because, as her husband observes, they have similar personalities. Mrs. Ayase seems to have a sweet tooth, with cravings for ice cream, cake, and other desserts.
Mr. Ayase (????? Ayase-ke no Chichi)
The father of the Ayase sisters is almost never at home, at least during the day. While his profession is not revealed in the series, it appears consistent with the life of a salaryman. Asagi mercilessly teases him about his constant absence (in Chapter 14, she laments that "Dad isn't with us anymore", whereupon Fuka corrects her, saying, "He's not dead, just at work!"), but he seems to have a good relationship with the rest of the family. He has a very laid-back and sentimental personality.
Friends
Takashi Takeda ("Jumbo")A friend of Koiwai and Yotsuba, having known Koiwai since childhood (as indicated in chapter 31). He helps the Koiwais move in, and may have had a role in arranging their move to the city as he lived there already. Standing at 210 cm (over 6'10"), he dwarfs the other characters, especially Yotsuba. He is always called by the nickname "Jumbo," and when Fuka learns his real name she remarks that it is mundane. He works at his father's flower shop, though Yotsuba does not know this until she meets him there. He frequently visits the Koiwai house, and is more or less treated as a member of the family by Yotsuba.
Jumbo has a dry sense of humor and is prone to deadpan quips, which sometimes confuse the Ayases. At the same time, he is impulsive, and sometimes spontaneously organizes activities for the younger children. As he does this, he enters a bizarre one-sided rivalry with Miura (including spending a single day in Hawai'i after he learns that she will be going abroad). He also develops a deep infatuation with Asagi when he first meets her, but is too nervous around women to directly act on it. Instead, he tries to use Yotsuba's friendship with the Ayase family as a way of getting close to her, though his plans usually backfire. All the while, Yotsuba remains unaware of his ulterior motive.
Miura HayasakaA friend of Ena. She is boyish and brusque, both in her appearance and her way of speaking (this is very noticeable in the Japanese version), and can sometimes be too straightforward and insensitive. She also counters aggressively in a tsukkomish manner if she feels mistaken or made fun of. Because of this she appears less kind or thoughtful than Ena, but she is quick to notice others' feelings. For example, she immediately notices Jumbo's infatuation with Asagi and uses this to her advantage. Ironically, she is also extremely squeamish: when Jumbo takes the younger children fishing, Miura refuses to handle live bait, using salmon roe instead, and hides while Jumbo and Ena clean their catches. Miura often wears sports-related clothing and rides a unicycle.
Torako (??)
A friend of Asagi's, surname unknown, who seems to attend the same university. She smokes constantly and seems to be obsessed with being cool. Because of this she is often annoyed with Yotsuba's antics. Her name means "tiger child." She is the only member of the younger cast to own a car.
Yanda (???), actual surname Yasuda (??)
Yanda, given name unknown, is a friend of Koiwai and Jumbo. Though he is mentioned in the first chapter, he does not appear until chapter 30. Jumbo calls Yanda "no good" for making lame excuses for not helping the Koiwais move. When he finally visits, he tries to get inside while Yotsuba is home alone, making her extremely suspicious of him. He is somewhat childish, as shown by the tit-for-tat pranks he plays on Yotsuba, including bribing her with candy then taking it back when it does not work, eating her ice cream, and prank-calling her. Koiwai refers to him as his k?hai, but in what context he is Koiwai's junior is not yet known. Yanda is living from paycheck to paycheck, telling Koiwai that he eats instant ramen because does not get paid until the end of the month.