I don't think Hisao "begins" to develop it. It's just who he is. He tries to help people. It seems consistent no matter which route you take. It's just more obvious with some characters than others. He even tells Lilly in her route that he was the guy that used to break up the fights and arguments amongst his circle of friends.Hisao begins to develop this "White Knight" feeling throughout Acts 1 to 3,
It pretty much IS interfering with a normal life. She has difficulties with people when they walk past her for crying out loud.A lack of social skills isn't really a problem you help with. A problem implies it's something that can and should be treated and that is interfering with a normal life,
And she IS receiving help for it. She goes to a therapist on a regualr basis.
And this is what Hisao was trying to do for her. He wanted her to get out more and interact with people more. Not even necessarily strangers or anything. he made it perfectly clear that the two of them could just go out together where nobody else would be around.but Hanako's social awkwardness (Extreme though it may be) is something she largely overcomes herself simply by practicing social interaction with someone close by that she trusts so that she's a little less nervous about going off on a limb.
He just misjudged her and handled the situation poorly. As did she.
And if Hanako stopped locking herself in her room, they wouldn't have had so much trouble either. Want to make up more theories about what would happen if the two of them weren't acting like themselves?Hell, if Hisao had always simply acted as a friend and never told Hanako about his white knight tendencies, a whole lot of awkward situations could have been avoided.