Actually in a sense, it also mirrors Hanako's development.
Mirroring is a pretty accurate description of Hisao and Hanako in general. While several of the girls change Hisao to become more like themselves, on Hanako's route he remains somewhat like he is at the start of Act 1 because that's the emotional place Hanako's been in for years. She's kind of an exagerated version of Hisao in several ways...she rolled the misery dice and got a 6 instead of a 4 like Hisao. But the two share a VERY similar mindset overall. (though Hanako's is hidden between 10 layers of shyness)
Some of the parallels between Hanako and Hisao:
- Both are the only child in an ordinary household and neither is born disabled like Rin, Shizune or Lilly are. Both are only averagely social, preferring a small circle of friends to a big social circle. Both lose pretty much their entire life, including their friends, when the events happen that turn their life upside-down and leaves them scarred. (and hospitalized for a long time) As a result, they both become "broken people" and somewhat bitter about human contacts in general and both like to just live by the day without having any clear plans for the future.
- Hanako's panic attack and Hisao's heart attack also have some parallels. In addition to people who experienced a panic attack stating it kinda feels like a heart attack and can be just as terrifying, the results for both characters also overlap somewhat. Prior to his heart attack, Hisao was about to be confessed to, but afterwards the subject isn't brought up ever again. Prior to Hanako's panic attack, Hisao was playing with the thought of confessing to her, but afterwards he drops those plans and they remain in the fridge until Hanako sleeps with him. So both cut a potential relationship short, though in Hanako's case, not permanently.
- Their hobbies also overlap. Both like reading a lot and both picked it up for similar reasons and in similar circumstances. They're also both quite competitive in games. During the Risk game in Act 1, no matter what option you pick, Hisao states the outcome of the match matters to him a lot. Likewise, after being beaten at chess by Hisao, Hanako starts reading up on chess tactics in order to get the better of him later.
- Both have a lot of trouble sharing details of their past with others, even with their friends. The only way they can do so with one another is through a comfortable give-and-take.
- They both tend to withdraw when going through a rough time and tend to push away people who try to pry at the wrong time. An obvious example with Hanako was her bad end. But Hisao has a very similar situation in Act 1 where he feels like crap after his heart flutter on the track and Misha starts prying, resulting in Hisao blowing up at her and telling her to "piss off". It wasn't quite the same, seeing that Misha wasn't patronizing...just too dense to realize the person she was pushing to open up needed some space to get their bearings.
- The results of being dragged into a club by overbearing fellow students also has similar results on them both. After joining the student council in Shizune's arc, Hisao becomes a lot more confident and is quick to make plans about his future. Likewise, Hanako being pulled into the newspaper club by Naomi (who Hanako describes as loud and somewhat tiring, but nice...like someone else we know) results in her too gaining confidence and making plans for the future.
- In Lilly's route, Hisao becomes a lot like Hanako in several ways. They both like Lilly a lot, but are annoyed by her pity and mothering tendencies, but ultimately get used to it so they don't call her out on her mothering. The biggest parallel experience is their similar reaction when they're afraid of losing the person they love. Hanako defies her disability by stripping naked in front of Hisao despite her insecurities about her scars. Hisao defies his disability by running after Lilly despite his weak physical condition. In both cases, their desperate action appears to backfire severely at first, but ultimately results in a happy end when their loved one reaches out to them.
No doubt the bond that develops between them in Hanako's route is the result of them sensing a kindred spirit in the other. It's not unlikely that part of the reason Hisao's white knighting is so much stronger in Hanako's route than in Emi's is because Hanako's plight somehow feels more personal to him. (codependants trying to fix another person often pick people who remind them of their past in a way...like an alcoholic's daughter later picking an alcoholic partner and trying to fix him)