I was so invested and tensed up until I see two bear nipples pointed straight at me from a taxoderemy grizzly bear, but it's interesting to see that all these characters are messed up in their own way. (Ironically, the one time he isn't on a date with Kii-chan is the one time his daughter most suspects him of being on a date with her)
-The dad (Kosuke) was suicidally depressed before he met Kisaragi. His wife was dead, his daughter was estranged and his work was forcing him into unhealthy habits of devoting himself to it in order to merely provide. He was divorced from society and didn't have any support network to help him with this. It's not like he could see a therapist because he didn't have time, and Kisaragi opened up a new world for him to understand. He doesn't fall into temptation with Kisaragi, as she attempts to seduce him multiple times which he sees is wrong and says he doesn't want that kind of relationship with her. Sure, you could judge him morally for even attempting to engage with a minor (though 16 is the age of consent in most countries and nothing he's done thus far is actually of questionable legality), but it's more the story of mental health and he was in such a vulnerable place that it's hard to judge him for it as his life has undoubtedly improved as Kisaragi has begun to enter it more and more.
-Kisaragi herself is an interesting character as you can read into her starting a relationship as a way to escape her abusive and overly possessive mother. At least, it started out that way. Perhaps she did it because she knew it was provocative, controversial and seemingly against the traditional fabric to start a relationship with a man more than twice her senior, and that was her way of tasting any kind of freedom or liberty that her mother would squash on, as even to the most moral of people the temptation of what seems to be morally questionable or wrong holds its own attraction. Or, alternatively, she did it because she saw the state he was in and empathized with him. She felt like she understood the despair he was and wanted him to improve. Perhaps she didn't love him to begin with, but she's certainly grown attached now. What's even more interesting is that she's the instigator of all of this. She clearly isn't the one being manipulated or lead along by an older man, but she's the one who's trying to get an older man to fall for her and to try and amend the situation at hand. Because this is the complete inverse of the typical story that's told of why younger women shouldn't date older men, it provides an interesting dynamic that immediately makes that claim fall apart.
-Ichikawa herself does have ample reason to be upset by the prospect that her best friend and her father are dating. It's completely understandable why she would feel not only betrayed but feel as if this situation was wrong. Devoid of context, she seems to be in the right on the face of it. But, this only shows to demonstrate how good of a job the author did at making us feel for the characters of the story. We know that Ichikawa was on the verge of being kicked out of school and hardly ever left her room. Every time her dad extended an olive branch, she wouldn't respond because of how the death of her mother affected her. She has been doing her work, but just enough to scrap by. She didn't notice her father's struggle because of her own mental health issues and so she seems selfish, but at the same time, he was so caught up in his work trying to provide for her that consoling her is difficult, especially as he's not over the death of his wife himself. It wasn't until Kii-chan showed up that the two were able to reconcile, though their relationship is still rocky at best, and she's able to deduce that there's something going on between the two of them. Her love interest, Misaki, is interesting as he's also a loner who hangs out by himself. He's implied to be a delinquent because he smokes as a minor and acts rather brazen, but they're drawn to one another because of this. She can immediately empathize with how disenfranchised he is and it solidifies the connection the two have.
The author is absolutely amazing as they were able to construct such an intricate but understandable and completely justified set of characters with complex relationships to one another and motives that would all be justified from their own perspective. I'm really invested into seeing how this unfolds, especially after the bombshell reveal of this chapter and I wonder what's going to happen next, especially with the secondary potential love interest in the coworker.