One night, before they started going out, Mizuto and Yume were in adjacent rooms on a middle school class trip. When they both looked out their windows at the full moon, Mizuto said Tsuki ga kirei desu ne, which means “The moon is beautiful, isn’t it?” but can also be an artful way of saying “I love you”. It’s a night Mizuto still hasn’t forgotten…even though it must’ve been more than what, two years ago?!
Fast-forward to the present, and Mizuto is being a big ‘ol jerk about not wanting to go shopping with Yume for Mother’s Day, even though they had plenty of fun on their date the other day. Yume convinces him to come with a fetching ” ooting” outfit, and when they’re on a crowded train and a bump causes Mizuto to pin her between the side of the car and him, she tells him not to pull away, as it will only keep happening with every bump.
The two settle on a bouquet of carnations, which is a pretty standard go-to Mother’s Day gift. But their mom is so happy to receive them that she runs away in tears. As we know, these are good kids, and making their mom/stepmom happy makes them happy. Mizuto may put out Ayanokouji vibes, but he’s nothing like that sociopath!
That evening, Yume notices the door at the end of the hall is open a crack – a beam of the setting sun gleams through, lighting motes of dust in the air. She finds Mizuto inside, praying to his mother’s shrine. Mizuto’s mom died when he was very small, such that her shrine photo is is only visual link to her.
Not only aware this is no time for sniping but genuinely wanting to support Mizuto during a lonely moment, she cuddles up next to him, like a “big sister” should. That’s when Mizuto says that since their parents are newlyweds, they should give them a night alone sometime. That of course means the two of them would have to spend the night…somewhere else.
Yume turns all sorts of shades of pink and red as Mizuto runs by what’s possible and not possible, even admitting to looking into love hotel rates. But since they both know that might just be taking things a bit far considering their history, Mizuto instead asks Kawanami if he can spend the night at his place.
Yume, in turn, can stay at Minami’s…because Minami and Kawanami are not only childhood friends as we all suspected, but also next-door neighbors. Due to that prodigious amount of time so close to one another, they’re basically more siblings than Yume and Mizuto.
Kawanami has a little fun with the paper-thin walls by acting like Mizuto is talking about Yume’s boobs (causing her to attack the wall), while Mizuto gets payback by reading Kawanami’s elementary school report on wanting to be a police officer so he can marry Minami (causing her to attack the wall).
Kawanami and Minami’s easy, lived-in rapport carries over when they both independently pick the same family restaurant to take Mizuto and Yume to dinner. Kawanami and Minami each know exactly what the other is going to order, while the two even have a shared laugh at the stebsiblings’ expense when they both show they have no idea about soda fountain protocol.
After dinner, Minami gets all cuddly with Mizuto about tutoring her in Japanese, but Mizuto shuts her down by declaring that Yume is the far more appropriate choice for a tutor since she “works so hard” for her grades while he puts in very little effort.
Later that night, Kawanami is bored that Mizuto is just studying, so he texts Minami, which again seems like a common occurrence. They may say they have nothing to do with each other, but they’re fooling absolutely no one—including themselves.
Kawanami and Miniami are so in sync they even fall asleep at the same time, while Mizuto and Yume go out on their respective balconies to admire a full moon. When Mizuto hears Yume on the other side he peeks over to find her in cute frog jammies Minami “made” her wear.
Then Yume says “Tsuki ga kirei desu ne”, confirming she too remembers that night of the school trip when he dropped that “pretentious come-on”. That said, she basically admits that was when she started liking him. Mizuto says there’s no point in telling him that now, but it’s clear he was happy she remembered that night as vividly as he did.
They both ponder whether all the time Kawanami and Minami have spent together “means” anything, being so close together for so long. As for the two of them, Mizuto believes it isn’t likely their folks will split up, so they’re “stuck as stepsiblings until the end of time.” While he tries to make that sound like the same “hell” Kawanami claims living beside Minami to be, both of them are vastly overstating their torment.