I can’t explicate based on logic as to why I like High School of the Dead, but I can unequivocally say I love it. Much of that love is towards Busujima Saeko, who, aside from being terribly attractive, can fight and is very useful. I mostly love High School of the Dead because of her.
Most of my top anime involve love stories: I’m really just a guy who likes a well-told romance. While romance is not the focus of High School of the Dead, there is an explicitly implicit tension among Saeko, Takashi Komuro (the main protagonist), and Miyamoto Rei, a close friend of his in the past. I recognize that the creation of a couple probably isn’t even in the mind of the mangaka writing the story, but if I were to choose, I hope that the ending will have Takashi and Saeko as a couple.
First, I understand that Rei has suffered much due to Shido’s actions. She had gone back a grade even though she was an excellent student, and to her, Takashi wasn’t around to comfort her. It can be implied that Takashi probably told her to face reality, as he was never the kind of guy (as we see more and more of his character) to placate women: he’s more of the guy who tells it straight even if people don’t want to accept it. Rei explains that she got tired of waiting for him, and as Hisashi was a more caring guy, she just went out with him instead.

I utterly loved this scene.
The problem I have with this defense of Rei is that if one really loves someone, one doesn’t let anything limit him or her from expressing that love. The same can indeed be said of Takashi, but I think any guy would get turned off from a girl who acts bitchy towards that guy, even if he tries to understand that girl. Rei did not clear things up and she did not have any intention to until Hisashi died. This alone is enough to condemn her actions. Had she truly loved Takashi, she would have told him straight up that she was struggling with the events in her life and that she loved him despite everything. She didn’t do it.
But Takashi is a guy! He should be the one to make the first move!
The problem with this is that you don’t want to anger a raging lion. Rei verbally abused Takashi, and it showed even in the post-apocalypse. Any guy would be irritated, if not downright pissed off with being cursed and bitched upon, and I think Takashi just walked away. Takashi may have problems with his ability to show his feelings, but Rei had the bigger problem with the inability to control it.
As I see it, it was Rei who traduced upon their pinky promise. Takashi just suffered quietly and persisted. Not even her current flirting or words could change what happened in the past.
In contrast, we have Busujima Saeko.
Saeko is pretty much someone newly introduced to Takashi, and were it not for the apocalypse would probably never have been acquainted with him. Saeko is pretty much the positive antipode to Rei: she’s quiet, deliberate, and cunning, but she also has her problems.
This is purely personal, but I think she is more physically attractive than Rei. Having said that, I admire her qualities, both good and bad, as evidenced more clearly by the ninth episode of the anime series (and the later chapters of the manga). I do believe that there was only some attraction to Takashi due to his manliness, but her feelings developed later on and was made more obvious in the anime counterpart of the series.
She is not needy, unlike Rei. Most of her conversations with Takashi end up pleasant, with her not asking anything from Takashi. In her emotions, however, it is quite obvious that she is invested with Takashi, and it only becomes more and more perceptible as the series progresses.
Much of her character can be deduced from her sharpness in understanding other people: during Rei’s recovery in the Takagi house, when Rei was flirting with Takashi, she quietly waited outside and for her turn. In the anime, this was after that night in the temple, where maybe something more than saliva was shared between them. Did she berate Takashi? She just entered and stayed quiet.
She understands that it is the apocalypse, and that loyalty between a man and woman is pretty much very difficult to maintain. So what does she do? She recognizes that she is a woman, and if there is ‘anything that Takashi needs, I can present my womanhood (paraphrased).’ It’s the kind of love that is not suffocating or wanting, but ever-present. It’s that kind of love that is quiet and pensive, yet passionate. It’s a love that’s quite opposite to what Rei currently shows to Takashi: it is devoid of jealousy or of need for compensation.
This happened because Takashi saw her true self and accepted it (maybe in more ways than one). Her simple recognition of who Takashi was and her acceptance of him and her self is just a delight to watch. Besides, it would be a more special ending by going against the grain, right?