Shinobu and Alice sit outside observing the flowers when they happen to overhear Yoko speaking. Shino gets up and runs over to Yoko while addressing her using older sibling terms, only to snap out of it and apologize for her mistake before running off in embarrassment. Only to grab onto their teacher and call her Mom.
In class the girls try to make Shino feel better by saying she made a simple mistake and it isn't a big deal as Yōko recalls having known Shino since elementary school. She was very antisocial and nervous and always tried to look for Isami to make her feel better when one day, Yoko took Shino to find Isami and seeing how they got along, Isami requested that Yoko watch over Shino since she worries about her. She gave Yoko a personal alarm for use in case anything would happen.
Later on, in that day, Yoko walked Shino home from school. She had realized what Isami said earlier and decides that she will protect her in place of Isami when she realized they were being followed; although it was only Isami.
After the story concludes, Karen mentions that Yoko is like a big sister. Then she teases Aya by saying she is just an Aya. Their chat is put on hold until class ends, when Shino requests Aya's help studying after she finds she got a zero on the recen test. Aya agrees and has Shino sit down and everyone watches as she explains that a make-up test will be held. So they begin to study the material and Aya scolds Shino for her use of "Fo' sho", with Shino admitting that she thought it was for the test. The others ask Aya for help studying as well and she agrees, suggesting they hold a study party.
Once school ends the girls meet up a Shino's and greet Isami, explaining why they have shown up. Aya hands her a large back of snacks and item she purchased for them all to share while Karen requests an autograph from her. She claims to be a fan of Isami's having seen her in magazines.
The girls head into Shino's room to study and Shino asks for help- only to run to Isami. Isami asks for something special from her sister first, but turns down the mask Shino offers to her. Eventually the girls stop for a lunch break and they comment on how Aya would make a good wife, after it turns out she made the food they're snacking on. After taking a bite to realize it isn't very food, Yoko attempts to spare Aya's feelings as Alice and Karen flat out tell her it's lacking in flavor. Yoko is taken back by their blunt attitudes.
Upon finishing, Karen decides to sneak into Isami's room and spots her camera nearby. Just as she approaches it, the older girl returns and finds her, causing her to panic until Isami claims it's okay. She grabs her camera and returns to the others with Karen, and tells them that while she likes to have her picture taken, she enjoys taking them more, and asks that they pose for her so that she can. However, the girls struggle to pose naturally in the small bedroom, so she decides to take them to the nearby park.
Isami comments on how much Shino has grown as of late as the girls seat themselves. She then tells Karen to start posing, although she instructs her to do it naturally as Yoko requests a picture of Aya with Isami. After several changes, they finally get the pictures they desired.
Later on the girls prepare to leave. They ask that Isami shows their pictures to the people she works with and she teases them by saying she isn't very sure if she should.
The following day, Isami is showing a friend one of the pictures she took. The friend asks what it is like having Alice live with them and she compares it to having two cute little sisters. She then takes a moment to discuss how much she worries over Shino, due to her absent-minded nature, but lately she finds herself worrying less and less because she has finally become passionate about something, but even now she worries over her future.
In class 1-B, Aya comes by Yoko and brings up her lack of dressing properly for class. Yoko claims that she will for important ceremonies and events though, but Aya insists that she dresses right, and now, and tries to fix her outfit. Yoko gains some mature compliments after, but this makes her wonder what she is normally thought of. When Alice and Karen join them later they are unable to recognize the sudden change in appearance, then they decide to arm wrestle. Alice has a lot of difficulty and Yoko decides to let her win- only to accidentally inflate Alice's ego and frustrating Yoko. She decides to give her a few fighting pointers afterwards to prevent her from doing something stupid.
Karen carries a heavy stack of books when Yoko comes by and offers to lend a hand. But Karen refuses, because she wants Yoko to carry her and the books. When they arrive to class, Karen points out that Yoko is very reassuring and compares her to a convenience store.
Yoko finds Shino troubled over something. She explains that Isami almost threw away the papers that she saved from an overseas trip. Then Yoko overhears Aya coughing and mentions a slight cold she gained. As Yoko makes an attempt to touch her forehead, she gets smacked by Aya and hands over a facial mask she can put on. This causes Karen to continue to pretend she is a convenience store.
By now Yoko has become frustrated and asks what the girls think of her. Shino suggests they make a pie chart and they find that it is a single piece labeled "Comedic Retorts". It's then Yoko catches Karen staring at her and finds out she's been making a brand new pie chart; which is actually the original one, but now cut in half to reveal the other half says "kindness". This flatters Yoko and Karen reveals the two-sliced chart she made for Aya, with one side reading Intelligence and Shyness, while the other half is Yoko. Aya is beyond angry and she destroys the chart as Yoko asks if she may have a fever, causing Aya to rip off the mask and storm off.
The girls resume discussing Shino's slip up from the other day and mention that they are all single children. They all then decide they would like to have an older sister as well.
Later on in class, Shino asks their teacher if she has any siblings. Sakura reveals that she is the youngest of three, as she has two older brothers she adores dearly and still addresses with childish terms.
After class Yoko joins Shino and has started to feel un-needed by her, as she doesn't get distracted as much. The same thing happens when Aya approaches Yoko and admits to being sad, because Shino isn't dependent on her. Then they claim that Shino would be fine no matter what might happen to her, when Yoko suddenly points out that their examples and theories to prove this are a bit far-fetched, so they make little to no sense. The girls recall a moment when Yoko was younger and she asked Isami if she could call her "Isa-nee", since she felt like an older sister to her.
Later on Shino takes Alice to where her sister was originally scouted. They decide to sit by for a while, to see if the same thing happens to them. But nothing happens and they are found by Aya, who mentions that she thought they already left.