Yotsuba might even get in for free. She’s only five, after all.
Koiwai’s pretty much a non-entity in this chapter. Ena, too. It’s mostly a Jumbo-Fuuka chapter.
The chapters tie together quite a lot. Like, it’s literally intended to be a day-by-day depiction of Yotsuba’s life. Pretty sure I saw a page once where they calculated the exact timing of each chapter, but I can’t find it now. Also, spoiler alert, the chapter after next features Asagi handing out souvenirs from her trip.
It’s on the Wikipedia page. Based on it, all 13 volumes have taken place in less than a six month period.
An SRS I’ve been using just taught me “revision” as 復習, which is a different terminating kanji than “revenge” 復讐. A timely coincidence. 
So, not chapter related, but I bought a tenugui from one of my favourite shops, and now I will be slightly less embarrassed when I read よつばと！on the train.
Struggling to understand Fuuka at the bottom of p. 122:
セクシーさに見とれちゃいました？
I know セクシーさ is sexiness, but I can’t work out the grammar of the verb phrase here.
Oh yes, and also don’t understand Jumbo’s reply (やるじゃん！) on the next page.
I haven’t studied this, but I broke it down like this:
セクシーさに見とれちゃいました？ → 見 + 取れる + ちゃう (+past tense)
See + able to take + accidental/unintentional verb ender
“Were you able to see (+take in, +unintentionally) my sexiness?”
EDIT: 見とれる is actually a verb on its own, which means “to be fascinated”, so this is actually “Were you unintentionally fascinated by my sexiness?” 見とれる + ちゃう (+past tense)
I don’t know precisely what やるじゃん means, but it’s like やる + じゃない with the connotation of “You do it (i.e., look good), don’t you?”
I hope someone can correct me.
I also understood something like that from じゃん.
It’s an expression that I understand to mean something like “Way to go!” Jisho also has it listed as meaning “not bad”.
Well, I’ve just given chapter 12 a read through, but sadly I’m much too busy this week to give it a close reading, and too busy to post all my usual dumb questions! And though I loved a couple of things about this chapter (the visual joke on p.116 when it’s Fuuka and Ena turn up and not Asagi, and the funny picture of Jumbo throwing Yotsuba on page 127), I think this has been my least favourite chapter so far from the two volumes. None of the characters showed a particularly good side to themselves and to be honest I didn’t much like them as a group of people. There didn’t seem to be much fun about it this week. But, like I say, I could only give it a quick read and so certainly missed out on loads.
Looking forward to having more time, and a deeper reading, in next week’s chapter!
Hah, let me warn you now, when I first read it in the English version many years ago, I hated the next chapter. It’s Miura at her most Miuraishness. She starts to improve after that chapter, but that one is easily her worst moment.
Ok, here is my list of questions about this chapter. I am sure many of them could be answered by the reading pack, but I do not have it, so sorry in advance for silly questions.
p. 112 panel 4 What does テキート mean?
p. 115 panel 1 What does ダシ mean?
p. 118 panel 2 What is Janbo saying? I get the gist of “You’re just a child!” but what’s happening here?
p. 119 panel 5 I’ve never seen ねー in this part of a sentence before. What’s up with that?
p. 123 panel 5 I’m missing the connection between “waist meat” and “maniac”
p. 129 panel 1 Who is saying the thing in the word bubble? Ena?
Apparently, if we are to trust this random blogspot site I found:
適当 Tekitou: This is a word that can have a good or bad meaning depending on the context and the values of the person using it. If it’s used in the negative sense, it can mean something like vague, unserious, or half-assed. In a positive way, it can be used to describe something done casually, quickly and without too much effort or stress. Relaxed or lazy, depending on the context.
Dictionaries say it means “Appropriate”, but the English translation of the chapter further convinces me of this approach. "お前テキトーな事言うなよ” becomes “Don’t say vague/half-assed things” (about not knowing what Water World is.)
Or perhaps it’s just “Don’t say appropriate stuff like that” (about Yotsuba usually being more random or exaggerated in her speech and mannerisms.)
Couldn’t find anything about ダシ. 
As @BobaGakusei said, on the vocabulary list 出し is explained as Pretext.
引っ込む: to withdraw (e.g. from the public eye), to retire to (somewhere), to stay indoors, to butt out, to stay out of it. “Children should stay out if it!”
私ねー is pretty common (said by kids) from my experience, something like: “You know, I…”
Even though she has a little too much meat around the waist, that’s fine with a lot of people. (Or, there are people (maniacs/enthusiasts) that like it that way.) マニアックで良い.
And yes, it should be Ena saying that.
A really fun chapter as always! If not for your questions I wouldn’t have paid much attention. 
Fuuka cover on the next one. 
Yeah, it’s Ena. Aside from the use of the kanji, if you pay attention to the conversation flow, it makes sense.
Page 128 final panel goes
Ena: “Wow, you’re a really good swimmer, Yotsuba-chan”
Yotsuba: “Yeah”
Page 129 first panel
Ena: “Me too. I can already swim 25 metres”
When WK teaches it (level 30 https://www.wanikani.com/vocabulary/適当), the description includes this: “Strangely enough, this also means irresponsible.”
For what it’s worth, that’s how I interpreted it as well.
I didn’t understand at first how saying “知らなかった” was something bad.
But now I see that she first said “あれなー” implying she knew about it. 
Here are some questions related to swimming.
When you were a child, could you swim? How about now?
Are you good at swimming? Do you like it? Where do you usually swim?
Have you been to a place like Water World? Was it fun?
(A silly question. Personally, I still haven’t gotten over the fact that there are two words that mean swimming.)
Between “すいえい” and “およぎ”, which of the two words do you prefer? Why do you feel that way?
How do you decide between Verb+の and Verb+こと?
子供の時、水泳のクラスがありました。今泳ぎできてがあんまり泳ぎます。
上手じゃない。おぼれない方を知ります。楽しいです。
故郷で波のプールがあります。ウオーターワールドわちょっと「エクストラー」と思ういます。
最初に「泳ぎ」を習いたので、「泳ぎ」が好きです。
If my answers are less than perfect, I should hope they are at least comprehensible.
