This episode opens with a flashback to the lake incident before showing Mariko, back to school from the holiday, reciting Matthew Arnold's "Requiescat" in English class. I should clarify here that the summer holiday they took wasn't full-time summer vacation, just an extra-long weekend because of their school's founding anniversary.
Mariko and Kaoru both look towards Nanako's empty seat. Nanako is faking a fever to avoid going to school.
Fukiko approaches Tomoko and Mariko to ask about Nanako's absence, and gets the sick excuse from them. The contrast between the facade she's presenting to Nanako's friends and what she's capable of makes her blacked out face of doom creepier than normal here.
Tomoko brings her some cake after school, and they go down to the beach on Nanako's request. Tomoko is like "Oho, I figured you were faking it", and Nanako gives her an omamori she brought back from the trip as a souvenir.
Tomoko asks if something happened on the trip because of Fukiko asking after Nanako today. Nanako plays it off as a perfectly delightful trip, but Tomoko can tell something is amiss.
When Nanako gets home, her mom lets her know she's got a call from Fukiko, since Fukiko is nothing if not persistent. Nanako has the least surprising look ever
Back in her room, she stares at her phone like it's a hissing cockroach before taking it. Fukiko asks her about how she's feeling. After Nanako lies that her fever's gone down, Fukiko is like
Here I take a break to eat a kouign-amann from Crumble & Flake. It's so fucking good. (My girlfriend Amy: "It's like bread candy.")
To answer your question, gentle reader, about why Nanako doesn't just tell off Fukiko for being a horrible bitch: Fukiko frightens her, as evidenced by her physical reaction to interacting with her. Most crucially, I think, Fukiko also gaslit her in this scene and right after the near-drowning, making it seem like, contrary to how Nanako might have interpreted it, the near-drowning wasn't a violent assault, just a prank- or at least, that Fukiko has a story that can contradict anything Nanako says otherwise. "Why doesn't Nanako switch schools?" Easier said than done at this point in the school year and it would still unfairly punish her in a way. I'm not saying Nanako should stay at Seiran with all this bullshit, just why I can see why she reacts like she does.
Amy also adds "Oniisama E is like sad Glee with no music", what with the heightened-ness and the utter ineffectiveness of its adult authority figures. Oniisama E's writing is too consistent to be too similar to Glee, though.
The next day at a café, Mariko and Nanako are having tea and Mariko's like "So, what are you getting Our Lady and Savior Fukiko for her birthday?" Apparently getting Fukiko a great birthday present is to Sorority members what the Hunger Games are to the citizens of Panem.
Later, Nanako and Tomoko window-shop a fancy jewelry store. For once a brand is referenced in anime without its name being changed.
Nanako keeps looking for jewelry she can afford, and Tomoko suggests that instead of focusing on cost, she give a gift that only she could give, like her fabulous cookies. Nanako doesn't want to repeat what she gave Mariko, but hey, if it's good enough for her friend, it's good enough for the asshole who almost drowned her.
The next morning, Rei bring flowers to her mother's grave for the anniversary of her death.
Oniisama E being what it is, you know this party won't go off without a hitch, though. The scene transition music knows it, also.
At the party, Fukiko sits as guests present her with gifts one-by-one. There's even some kneeling, in case the queen-receiving-tribute aspect wasn't clear.
Nanako is embarrassed by her homemade cookies and their lack of exorbitance. Nonetheless, Fukiko seems happy with them. I assume Maria-sama ga Miteru's Oyuki Konno had this scene in mind when she wrote the birthday gift scene in Maria-sama ga Miteru: Vacation of the Lambs--where Yumi had to give Sachiko's grandma a birthday gift in front of a party of rich assholes and pleased her with a simple gift, a song she sang.
Apparently this was just the Sorority-only portion of the party. More people are arriving in thirty minutes, and first-years are to prepare the reception room by then. After guests arrive, the first-years take up their positions hostessing and serving food and drinks.
Takehiko and Takashi arrive, and Nanako, apparently not heeding Fukiko's desire for her to have no communication with Takehiko, walks right up to greet and thank them for hosting her and her friends at the university festival. When someone knocks into Nanako, causing her to spill a drink on Takehiko's suit, she starts trying to clean it with a handkerchief, causing Fukiko to glare and walk over to send her away for more drinks. It's kind of like Cinderella, if Cinderella's stepmother wanted the Prince and Cinderella was more interested in a chick. Apparently Takehiko showing up is a surprise, and he unwittingly gives Fukiko the most lesbian of flowers.
Nanako gets some more drinks and comes across Rei.
Despite Takashi's game attempt at making the party still work, the guests leave, since there's no recovering from a party's hostess acting like a homicidal five year-old. Takashi offers Mariko a ride home and Takehiko starts to walk Nanako home, but Mariko has Nanako walk home with her. Rei walks alone, un-umbrella-ed in the rain, Nanako and Mariko find the events of the evening too shocking and weird to talk about,
birthdays always end horribly.
Fukiko also burns Nanako's cookies and Takehiko's flowers in a furnace, so I guess she's starting to get pissed at him as well for his culpability in... uh, pleasantly interacting with Nanako.
Next episode, Rei asks Takashi if there's a story behind Fukiko's actions, and we get the whole enchilada.