Hikki and Yui are asked to take a look at the practice prom pictures and choose which to use on social media. Hikki leaves it to Yui, who makes sure to pick a couple of nice shots of her and Hikki dancing. After that, when they ask what’s next, Yukino tells them that’s all for now; the StuCo will handle the remainder of prom preparations, but she’ll reach out to them again if she needs any additional help.
Since neither Hikki nor Yui are busy, they decide to hang out together, with the ostensible mission of buying a gift for Komachi. Hikki geeks out at the new coffee vending machine, and the two end up in an IKEA showroom, which is a repository of various living spaces meant to inspire and entice customers. It’s apropos that Yui mentions the future and the dreams they both had as kids in such a place, where it’s never entirely possible to forget that the places aren’t real—only life-size dioramas.
That said, things seem to be going well with the prom plans until they’re not, by no fault of Yukino or Iroha. Yukino and Haruno’s mom represents members of the PTO (this schools version of the PTA) who are bristling at the idea of a prom after seeing the pictures, believing it to be “unbecoming” of high schoolers (clearly they’ve never been to an American high school dance!).
They want to cancel the prom, and Iroha’s impertinence in protesting that position and splitting hairs with the “initial consent” doesn’t help their case. Hikki can tell that Yukino’s mom is no joke, but he still reflexively tries to help by getting the school’s more positive opinion from Shizuka, and Haruno accuses him of being the “big brother” again. Yukino herself wears a defeated smile, telling Hikki if she accepts help whenever he offers it, she’ll eventually become “useless”.
Haruno later tells Hikki that his self-described “love triangle” with Yukino and Yui is really a triangle of codependency, but she’s letting her deep pessimism overlook the progress the three made. Yukino’s main issue is that she’s decided to shut Hikki (and Yui) entirely out of the prom, believing it the only way to demonstrate to her mom (and herself) that she can do it On Her Own.
That’s pretty damn harsh, if you ask me. People, be they high schoolers or adults, help their friends out when they need help! While I understand the moral objectives of a few parents (without agreeing with them), I find this absolutely-no-help, hands-off edict regarding Yukino…distasteful. No one person can organize a prom on their own, period!
What it comes down to is the reason Hikki wants to help, which is that he truly cares about Yukino, not because he needs or seeks anything in return. He and Yui are about to make some homemade cake for Komachi, but Hikki is drawn away by a text from Iroha indicating the PTO has gone forward with cancelling the prom outright.
Hikki calls Shizuka for the skinny, but she makes sure to ask him the reason he wants and needs to get involved, and after briefly clamming up, he tells her: because he “promised to save her someday” (which he did in season 2, episode 9). It’s as simple as that. When Yui hears that, and Hikki prepares to head back to school, a couple of tears fall, then stop; she claims they’re out of relief.
As Hikki runs away from her and towards Yukino, the tears start falling again, and they won’t stop. Part of her wishes they hadn’t stopped when they did, since Hikki might’ve stayed. But between Hikki running off like he did and the photo she found in Yukino’s room, the love triangle Hikki mentioned is looking more and more like a straight line.