nahh i think 'hikaru' as a being that a human cannot understand is simply doesn't have any 'human awareness/ morals/ consciousness' without the human body/brain, since he's just a soul/unknown entity that doesn't even understand the difference between life and death without it. what he was doing—as an unknown entity that is not tied by any human moral and norm, is quite understandable bcs in that state he was even about to consume yoshiki (someone he loved the most, and the very last person he wants to kill when he's in the human body) if it's not bcs of that stone protecting yoshiki's soul. it was all bcs he—as that unknown being, needs to fulfill the wish but the only way to go to the other side is to eat the soul connected to him, and when he saw a chance (the girl's soul that made a connection with him) he grabbed it without thinking bcs he didn't have any human awareness as a mere soul.
True, but I think that now he’s had human experiences, he has a reference point to the state he was in before he became “hikaru”. He didn’t know he was lonely before becuase he never knew anything other than that, if that makes sense. So I think from this perspective, his growth as a character is centered around the theme of loneliness. There was also something about the entities of his type wanting to be around where humans are, so I think these entities by nature are things that yearn to not be alone
Since "Hikaru"s only real understanding of human emotion is loneliness, I think he understands death is bad because it makes others lonely and sad (hence why he didn't kill Asako, because it would make Yoshiki sad) but in the case of this girl, Yoshiki's wish (to not be lonely) trumped everything else. I feel like this is where the story will really start to pick up heavily, like Yoshiki will be distraught with guilt and make another "wish" for "Hikaru" to save the girl, but when he does it'll just be another consequence that they have to chase after