Throughout the episode Adachi is on edge until she achieves her objective: ask Shimamura to hang out with her for Christmas. Because she knows it will sound like asking her out on a date (’cause, well, that’s what she’d be doing) and thus change the complexion relationship forever, she struggles to find both the right time to ask and the words to use.
Her first opportunity comes when she asks if she can study at Shimamura’s place. This means Shimamura turns down an invite from Hino and Nagafuji, whom we learn have grown pretty darn close themselves, as Nagafuji for all the world looks like she’s about to kiss Hino on the lips before moving to her forehead.
Up in Shimamura’s dusty study room, she and Adachi get under the kotatsu, and Shimamura calls for a break while the room heats up. Rather than ask what she needs to ask, Adachi instead asks what kind of kid Shimamura was. Her answer is that she was pretty normal; her hair was shorter and undyed, and she wasn’t as inhibited.
She then nods off, and Adachi leans in to almost kiss her before withdrawing, only to have her lap commandeered by Shimamura once she wakes back up. Shimamura doesn’t explain why she’s so comfortable placing her head in Adachi’s lap, and Adachi is far too happy about it to ask why—or about Christmas. She just enjoys the moment for what it is: pure bliss.
The second half of the episode is from Shimamura’s perspective, and she lists all the weird things about Adachi lately. She’s constantly staring at her, always seems like she’s keeping herself from saying or asking something, and even got a higher grade on her English test. That last one is neither here nor there, but it’s proof that Shimamura has had a positive influence on Adachi’s academics.
Shimamura determines if Adachi can’t get the words out, she’ll have to help her do so, taking her by the hand to the roof for some deep breaths and to ask straight up what she wants to talk about. Adachi blushes and says she’ll tell her “after giving it some thought” even though she’s thought of nothing else for days.
Adachi somewhat reminds Shimamura of another friend she had in primary school, who always hid behind her like a trusty shield unless they came across “something sparkly”, then ran to that. That was, perhaps, the first time Shimamura started to question the value of getting close to anyone.
Adachi ends up appearing at Shimamura’s door early in the morning before school. She feels Adachi’s face and brings her in to warm up and, hopefully, finally ask her what she wanted to ask. And at long last, Adachi powers through her crippling hesitation to ask, in almost too roundabout a way, if Shimamura will hang out with her on the 25th of the month. That’s right—she can’t even say “Christmas”!
When Shimamura considers the question, its phrasing, the manner in which Adachi struggled to say it and the redness in her face, she almost asks “why”, but stops herself, knowing it could well irreparably harm their present relationship. She’s apparently so jaded about meaningful bonds that even if she did wreck them, she can’t see herself putting in the necessary effort to repair it.
It’s only when Adachi senses Shimamura pondering her question that she rephrases it in a way that simultaneously fails to get her true feelings across and makes it possible for Shimamura to accept. Adachi says she wants to hang out with “someone” for Christmas, which Shimamura takes to mean “not me specifically, but I’ll do since I’m really her only friend”. Of course, we know Adachi doesn’t want to hang out with anyone else, just like she doesn’t want to kiss or hold hands with or lie in the lap of anyone else.
That said, once Shimamura accepts, she can’t help but see how goshdarn giddy it makes Adachi, as if a huge weight had been lifted from her shoulders. Is that really the reaction of someone for whom “anyone will do”? In her haste to start preparing their day, Adachi marches out of Shimamura’s house and bikes off without her, leaving Shimamura on the floor with her hand out yelling “Wait for li’l ol’ me!” in an uncharacteristic, old-timey way.
So yeah, these two aren’t quite on the same page, and at the moment Shimamura simply isn’t strongly considering the possibility of a romantic entanglement with Adachi in the near future. That said, if anyone can change Shimamura’s way of thinking about the matter, it’s Adachi. While her words continue to fail her, perhaps she can get the job done with her actions.