When she realizes there's a history between Yuu and Yami she takes steps to go talk to her friend, a courtesy that neither Yuu nor Yami extended to her
It was about time they tried to blame Yuu again, when of the three, he's the most innocent. Even though the novel makes it clear he didn't say anything because he didn't even know Hikari and Yami knew each other. Even though the novel makes it clear he didn't know Hikari saw the kiss. Even though he dropped several hints during his confession, inviting Hikari to talk about the kiss to see
if she had actually seen it.
At most, we could consider Yuu the more responsible of the two for choosing not to speak up after Yami's stolen kiss, but Hikari had plenty of opportunities to bring it up and SHE DIDN'T.
It's refreshing to watch her attempts to change from a childhood friendship to a romance without her having to resort to flinging herself at Yuu's dick.
Hikari is the exact opposite of Yami's actions, and even more harmful and nefarious. She is just as passive, if not more so, than Yuu. It is precisely her passivity and ambiguity that allowed Yami to have TWO opportunities with Yuu.
No one is saying she had to jump at Yuu's penis,
but she definitely could have been much more clearer and direct with him.
And the entire ED episode is there to make it clear that Yuu wasn't looking for sex, nor did he intend to ask Hikari for sex, just as he never asked Yami for it. He was looking for romance and someone who would reciprocate his feelings, as he himself says in his omake chapters. I haven't seen such a poor understanding of the character in a long time, even with the limited characterization we do have of him.
This is undoubtedly one of the few things Maruto has established as a defining characteristic of Yuu as the male protagonist.
I will not tolerate or allow Yuu to be treated like some lustful monkey.
Otherwise, no, Hikari doesn't really communicate with Yuu or try to ask him directly about his life, his past, or his romantic choices. It's always external events that motivate her to want to know more about him and ask him questions—just as happened to Yuu himself with Yami.
If Hikari would have been really open with Yuu about her own life, definitely Yuu would know the full name of the best friend of Hikari being "Ayami" and not just "Aya-chan".
The only time Hikari asks about it on her own initiative is when she asks Yuu if Seki is his ex-girlfrien
d. That, along with the fireworks episode, is the closest thing to Hikari actually communicating with Yuu AND THINKING ABOUT HIM INSTEAD OF HERSELF.
So far, Hikari has easily been the most selfish of the three main characters, and at the same time,
the most well-intentioned and the one who has done the fewest "bad" actions. You could say she's the embodiment of the negative golden rule: "don´t do to others what you wouldn´t want them to do to you", in her passivity.
Most of the time, she'll help others who are crying out for help, but she'll never move for someone who doesn't openly express their pain, because she's too insensitive to see it—as Yuu and Yami themselves mention several times.
She'll react with compassion if Yuu or Yami cry in front of her, but without that external stimulus, she's completely incapable of even thinking about them, let alone putting them above her own selfish interests. Hikari has never sacrificed anything or anyone. And to be fair, she doesn't have to, nor did Yuu ask her to. Simply being honest with her and asking about Yami's kiss would have been more than enough.
Hikari is a girl who walks through the world blind and is incapable of seeing things even if Haru, Yuki, and Yami herself tell her directly. Even if Yuu confronts her about her lack of concern for his academic future in middle school in his omake chapter.