What happened between Kaoru-tan's father and Hajime-kun? Kaoru collapsed from cigarettes and overworking, so I assume Hajime went to apologize to her father for pushing her too hard, while he can't find a proper job. I understand why Hajime would do so and why he thinks he deserves to be hit, but what would her father get angry about? I don't understand why he would even want to hit Hajime.
I guess I should post this as answer. As a father, you would want your daughter to have a good husband who has a proper job so she won't be having a hard time to word in order to sustain their needs. So Kaoru's father thinks that Hajime is not worthy of being her husband and that makes him very disappointed of Hajime.