Nagi agrees to help Erika study for her make-up exams as long as she stays focused, but let’s be honest: even he knew that wasn’t going to be easy. Erika cosplays in a military uniform (and dresses up Sachi too) and plays lip service to this studying “mission” to hold the “territory” of their house, but …she also just might have undiagnosed ADHD.
There’s also the matter of her previous rich girl’s school not being nearly as academically tough as Nagi’s, and even if it’s not Nagi’s fault her father enrolled her there, the fact it was done because they’re engaged lends him a measure of responsibility, so he tries to help her study, but she keeps getting hung up on things like why the symbol for Pi isn’t a cute emoji.
But after more than three hours of not getting through a single problem, Nagi is fed up, and reiterates that he needs to study too in order to beat Hiro. Hearing her brought up is the last straw for Erika, who gives up and skulks off to her room, apparently resigned to move back in with her parents. Nagi, too annoyed by the lack of progress, doesn’t stop her, and Sachi’s attempt at mediation fails.
Later that evening, Nagi realizes that he’s become accustomed to this place, and isn’t in a hurry to leave it, but that’s what will happen if Erika fails the make-ups. That would feel like moving backwards. When he goes downstairs for some coffee he sees Sachi crashing on the couch. She tells him that Erika is still studying, and he should help her.
When he enters her room (without knocking) Erika is sitting at her little desk lamp fighting back tears as she desperately tries to cram, so while Nagi’s sudden appearance is unexpected, it’s not unwelcome. When she asks why he’s helping her when he’s fine with her going home, he says her problems are his problems, because she’s his fiancée.
While Erika continues to prove a tough toutee, Nagi pulls two straight all-nighters with her, and he’s there in the classroom when she receives the result of their hard work and perseverance: her grade improved, and her dad calls off the summons. Erika and Nagi share both revel in their victory with wide smiles. Her text to her dad with the news, complete with eyelid-pull emoji, actually makes him happy.
As a reward for passing, Sachi invites Erika to the festival being held at the shopping district where the Uminos’ diner is. She’s late getting ready, and the folks wander off to mingle, so the family yakisoba stand is run by Nagi and Sachi. You can tell when Nagi catches her after she trips on her laces that Sachi is happy for some quality Onii time.
However, things get awkward with them again when Hiro shows up. Nagi introduces her, she remembers the text on Nagi’s phone about going on a date, and reacts coldly, turning her head and ignoring Nagi when he says she’s being rude. She’s also offended when Nagi so quickly agrees to walk around with Hiro later.
She assumed that Nagi would hang out with her and Erika, especially since this is in part a celebration of Erika passing her exams. It’s kind of cold and oblivious of Nagi too, considering Erika told him to think of Sachi as less of a little sister, and I thought it got through to him. Apparently not!
Naturally, before Nagi is done cleaning up the stand after they sell out of food, Erika arrives resplendent in a yukata lends one to Sachi, and the two head out without him and bump into Hiro, because of course they do! Not only that, Erika introduces Sachi as her sister, when Hiro had already heard that she was Hiro’s.
It’s weird to think that Hiro has never officially met Sachi, but then again she isn’t aware that Erika and Nagi (and Sachi) live in the same house, nor did she even know Nagi’s home was a diner. She and Nagi have been through a lot, but there’s still a lot she doesn’t know about him and Erika, and it looks like she’s going to learn more very soon.
Whether that new knowledge will change how she feels about Nagi “changing her fate”, or makes her feel betrayed and hurt, only time will tell. But I for one believe she’s been in the dark too long as Nagi’s “side girl”. It’s time for things to come to light and let the cards fall where they may.