I like your essay, though I think YusukeXKeiko is such an obvious couple that there wouldn't be any need to explain it. It's all there, in both the anime and the manga: they are in love, only a blind *and* deaf person could not notice it.

On a side note, I like Manga!Keiko much better than Anime!Keiko: there are several scenes in the manga in which Keiko shows her strong attitude, even by using force to beat the hell out of annoying demons. In the anime, those scenes are modified so that she loses a part of her attitude X(.