Here's a list of characters and related tropes for the manga series Yotsuba&!.
The Koiwai Family
Our viewpoint character, a five-year-old with a very energetic outlook on the world.
Adorably Precocious Child: Ziggzagged, there are times when she acts exactly like you would think a five year-old would act, then there are times she does or says things that you would expect from someone older. Though the things she says are sometimes played with as well since there are times its obvious she's just repeating what she heard with no idea as to the meaning.
Bad Liar: Not that she's noticeably worse than any other five-year-old. Props though, for trying to use A Wizard Did It.
Yotsuba will deliver Fuuka her milk, even if she hasn't a clue where Fuuka's school is, or even what a school is. Because a milkman delivers.
Also, when told to return home alive from "exacting revenge" she replied: "Even if I die I'll come home alive." And she did.That's determination.
Expressive Hair: Her pigtails rise and fall with her (rapidly changing) moods.
Genki Girl: In spades. And the trump suit. This gets Lampshaded by Asagi: "Her default rate of movement really is running."
Happily Adopted: She doesn't care one bit about her parentage. Koiwai is "dad" and that's that.
Hate at First Sight: Yanda tried to enter the house while her dad was away. Yotsuba was taught not to let any strangers in when she's alone. Which leads to her slamming the door on his face. The fact that Yanda enjoys making her angry on purpose doesn't help improve her opinion of him.
Intergenerational Friendship: Other than the recently named Mii-chan, Yotsuba doesn't have many friends her own age, with Ena and Miura being the closest in age at ten. Justified because she just moved to town and isn't in school yet.
Malaproper: She mostly knows the words, but how to say them is still a little beyond her.
Meaningful Name: It means "four leaves" as in "four-leaf clover". Thus her hair.
"Yotsuba" and "Koiwai" are also both brands of dairy products in Japan, and a whole chapter is centered around drinking milk.
Mistaken Nationality: Based on her appearance, strangers constantly assume Yotsuba to be a foreigner, and indeed she was born in another, unknown country. As a result, some students at Fuuka's school try to speak to her in English because all gaijin are American.
Parental Abandonment: We know nothing about her origins except that Koiwai found her somewhere overseas, which Yotsuba claims was "an island 'to the left'".
Sunny Sunflower Disposition: She's such a Genki Girl, she appears with a bouquet of sunflowers in the cover of the 1st volume. A later chapter even sees her fascinated by sunflowers in Jumbo's shop, and wanting to buy some.
Super Drowning Skills: Suprisingly averted, Yotsuba can swim quite well. Koiwai, Jumbo and Fuuka on the other hand...
Third-Person Person: Childishly, in the original Japanese (mimicked in the Yen Press translations); she combines this with an innocent imitation of her father's masculine language — the effect is hysterically funny but is, alas, Lost in Translation.
Trademark Favorite Food: As expected for a five-year-old, Yotsuba really likes ice cream. She also has a fascination for cup ramen. Curry is another favorite — one of the songs on the Image Album is called "Eating Curry (Very Delicious)".
Hypocrite: Despite his anger over Yotsuba lying to him, he himself frequently lies to her, though they are small white lies or pranks.
One of the Kids: He frequently behaves in a childishly over-the-top manner when interacting with Yotsuba, but otherwise he's a normal (if slightly irresponsible) adult.
Reasonable Authority Figure: He's quite willing to tolerate, if not participate in, Yotsuba's sillier antics. On those occasions when she does actively misbehave, the hammer comes down hard — sometimes overlapping with Scare 'Em Straight.
Unnamed Parent: We have never learned his given name. Even Jumbo calls him by his family name.
Jumbo calls him "Koi" on occasion.
Super Drowning Skills: He, along with Jumbo and Fuuka cannot swim, and will immediately drown when pushed into deep water.
The Slacker: He doesn't even wear pants in the summer, if he has the choice.
The Ayase Family
The Koiwai's next-door neighbors, frequently visited by Yotsuba.
The oldest Ayase girl; Yotsuba looks up to her (figuratively and literally). She seems to enjoy it.
Dude Magnet: Not that she notices, but Jumbo and Yanda both fall hard for her.
The Gadfly: Likes pulling pranks on people, or using Yotsuba to pull pranks on people.
Hidden Depths: She is actually really good at fixing Teddy Bears, even ones with a electrical voice boxes that had been soaked in water.
One of the Kids: She is able to follow along with Yotsuba's train of thought better than anyone else.
Romantic Two-Girl Friendship: Asagi and Torako do pretty much everything together, including going on long trips. Yotsuba's discription of the two's relationship sounds like they are girlfriend and boyfriend.
Sweet Tooth: She gets it from her mother. They sometimes clash over it.
Troll: Yotsuba spends a whole day excitedly waiting for Asagi to bring her a gift, but upon returning from her trip Asagi pretends to have no idea what she's talking about. Its not tell Yotsuba is dejectedly walking away that she pulls out a bag of fireworks.
The Unfavorite: She and her mother do not exactly get along, played mostly for laughs.
The middle Ayase girl, and the one who seems to have the worst luck. Her travails, of course, go right over Yotsuba's head.
Berserk Button: Don't call her fat or mention her weight. Just don't. Jumbo (and Koiwai) found out the hard way in the pool chapter.
Childhood Friends: Implied with Koiwai. In the stargazing chapter, he mentions that he's taking them to a field that he and Koiwai went on a field trip to when they were children. Also, he's probably the closest friend Koiwai has. Yotsuba seems to think that he's his only friend, as stated in Yanda's introductory chapter.
What the Hell, Hero?: Koiwai calls him out on using Yotsuba to try and ask Asagi out, though this fails every time.
Unrequited Love: He has fallen for Asagi pretty hard, but he can barely talk to her let alone ask her out.
Ena's friend, who's not all that nice to Yotsuba (though she doesn't actively try to be mean; she just doesn't have everyone else's patience). Hates slimy things, in contrast to Ena.
Bifauxnen: She has short hair and wears boyish clothes. When Jumbo first met her, he had to ask if she was a girl or a boy..
Brutal Honesty: She tends not to keep her opinions to herself, and once pointed out that Yotsuba's drawing is terrible, almost driving her to tears.
Cool Toy: She keeps amazing Yotsuba with various things, such as Heelies, a unicycle and a push scooter.
Jerk with a Heart of Gold: Miura has a tendency to play mean pranks on Yotsuba (e.g. appearing before the latter in an eyeball mask after discovering that Yotsuba is afraid of eyeballs), but despite this, she is good friends with Yotsuba and Ena.
Lovable Coward: She is easily frightened, and cannot stand bugs, snakes, frogs or anything slimy.
Miko: Was dressed for the part during the Autumn Festival.
Sitcom Arch-Nemesis: Jumbo tries to be this with her, though she only sometimes takes the bait.
Shorttank: She prefers sports clothing to tanktops, though.
Perpetual Poverty: He barely even has money to eat well (living on a diet of mostly instant ramen), at least until the end of the month.
Pet the Dog: While not as bad a guy as Yotsuba makes him out to be, he seems to enjoy messing with her a little to much. That said he is also the one who gets her out of her funk when she's worried about Duralumin, and shows her the awesomeness of bubbles.