I continue to be baffled by comments on this thing. Like, on one hand I get it, but on the other hand, I no longer do, because we're now into people calling Yami a homewrecker like... dudes, there's not that much of this manga to misunderstand.
So first part: from Hikari's point of view, she details how she's just started to fall in love with her long-time childhood friend. They are not together. They have never been together. She didn't even see him as someone to be interested in until about the year this manga takes place. Notable events include: a younger girl getting attached to Yuu, only for him to say he loves someone he met before he ever met the younger girl, something Hikari takes as meaning he's in love with her. Hikari talking about love to herself while engaging in small talk with Yuu when they're walking home. Hikari reading interest and love out of Yuu's interactions with her and when he's around others with her. A festival confession scene, where Yuu talks about how he never felt like he could ever match up with her. School festival invitation things, where she pressures him to go to her school even though he really doesn't want to. Then the Yami-sempai kiss.
Now the second part, which we all should remember. An intense romance between a girl from a broken home and a boy with normal aspirations, where his straightforward nature cuts through her gloomy worldview and lets her feel again. It gives her a place to belong. He loves her, she loves him. He gives her the strength to stand up to her sexually abusive stepdad, to go to school again, to not try and do compensated dating because she already feels worthless. To let her believe that she can be a normal person, have a normal life, take ownership of her future. She gives him the confidence and belief that he can do what he puts his mind to, that he's not some doofus who can't do anything right. They improve each other. It's storybook. But we knew it ended when we came in, now we know why. SHE broke it off. Because the courage he gave her backfired. Her mother was angry at her that she revealed all the terrible shit her stepfather was doing. Tried to commit suicide, blames her for that, too. Yami gave up. Decided she is unworthy of being loved and will never be anyone other than a failure of a daughter.
Right, summary out of the way. You noticing something? That maybe the person Yuu was talking about when he said he was in love wasn't Hikari at all, but Yami? That maybe the romantic tension Hikari was always feeling was her own, and all the things she read into Yuu's expressions and words were just her thoughts? That he has actually come to terms with the idea that he wanted to beat Hikari in something, and that's why that's what he chose to tell her, instead of it being some sort of matrix dodge of his true feelings? That Yuu didn't want to go to her school because he KNOWS Yami's there, and he doesn't know how to face her after what happened?
That Hikari's chapters might have been from the perspective of a losing childhood friend? Kinda fuckin' looks like that now, doesn't it? We've all watched this shit happen before.
The short chapters and focus on the female leads, rather than the male one, make this interesting. The medium and perspective have elevated the story and made its turns unpredictable and feel fresh. But it's shown its hand, man. The first part was "what do you mean its a little late" and the second part was "oh shit I guess it was huh." Now we see how it shakes out.
This shit ain't high art how are you all missing the plot points you've seen a thousand times. It's just from another direction!