Most of the first half of this episode expounds upon the daily grief, emptiness, and hesitation to care that Kou has felt every waking day since losing his mother. The manner in which he lost her: very slowly; while he was mostly alone with her; while working so hard to get good grades and a good job that he didn’t spend as much time with her while she was healthy; that he didn’t even catch signs that she might not be well, even though he was doing everything for her; that his brother told him to look after mom, and he failed.
These are the reasons Kou is the way he is, and the reasons he changed so much from the boy Futaba fell for in middle school. And for once, the show comes up with a metaphor for us: it isn’t so much how Futaba puts it: that the door to his heart is closed and double-locked, it’s that the door doesn’t have a doorknob or keyhole. He’s not just keeping people like Futaba and his new friends out; he’s trapped inside, and doesn’t know the way out of there.
Doorknob, lock, or no, Futaba is determined to break through that door no matter what, not just to let herself in, but to bust him out of the emotional prison he inadvertently built. Futaba is more determined than she’s ever been, to the point that Yuuri doesn’t really seem to have that much of a chance. She may know about Kou’s grief, but when push comes to shove she didn’t have the guts to do what Futaba does, descend upon him like a storm that will blow the door to his heart open.
As clouds gather in the sky, it takes grabbing Kou, falling upon him, and embracing him tightly, as well as finding the right words to convince him, but Futaba seems to finally make some progress, giving Kou the “permission” he’d always been seeking to feel for someone or something again. That no hole in his heart can’t be filled, even if it takes more than one, or dozens, or hundreds of smaller things to fill it. It isn’t going to be easy, but Futaba is there to stand with and support him in the gradual but necessary process of forgiving himself and moving forward.