Reading your thoughts on Invisible Helix has me thinking... have you ever considered Yukawa and Kaoru discussing having children? Particularly post Invisible Helix? I think it would be so interesting to explore Yukawa's thoughts (and troubles) surrounding this after the events of that book! I'd love to hear your thoughts.
Yes! I have and do think about Yukawa and Utsumi discussing having children, quite a lot more since Midsummer's Equation, and more recently, Kindan no Majutsu. I've written some ideas about that out a couple of times.
If I may answer your question by talking about visual canon first, I think it's no secret that Yukawa in visual canon has complicated~ feelings about children, that would make it difficult to contemplate having progeny. I could make a case on what we have seen there that if he allowed himself to examine all that the universe has told him, that he would want children. In the past, when he has contemplated the thought, he hasn't gotten past the thought the fuss of raising them is excruciating, and because that's a less than charitable way of viewing the effort that takes, he'd rather not. I think he's capable of understanding that he wouldn't be a good father and that has made him dismiss the idea. He also has some deeply buried concerns about bringing someone else like himself into this world.
Or, at least, that's what he's told himself in the past, but he's changed. The possibility exists that having children, with someone to help him, would be something good, something he can do for the future. Looking around to what's available, he'd see Utsumi and wonder if she wants children, but taking a partnership/friendship as they have into something where they have to care for a new life would be incredibly intimidating, even if he struck up the courage to make an appeal to her. As we've seen, he's actually traditional in his ideas about marriage, and even though different ways of co-existing and parenting together are possible, I'm not sure if he's gotten to the point of dissecting all the different data points and putting them back together in a way that would be acceptable to both himself and Utsumi. Once he did....
Yukawa of the visual canon, if he wanted children, would adopt not a baby but an older child, not someone the age of Shingo or Kyohei, but someone just a little younger than Kyohei. He'd find it the more acceptable of all the possible answers. He'd ask Utsumi's help, but he wouldn't depend on her. He'd do all his research on raising a child and make a Plan. He'd be scared out of his mind, but he'd do it. He'd believe he didn't have a conscious preference, but personally, I think he'd lean to wanting a girl, but only one child, regardless.
Yukawa of book canon, however? Has never given the idea of progeny conscious thought. He's been a single man with a singular mind, and wouldn't mind remaining that. It is only that, well, he's getting older and perhaps, maybe, he shouldn't leave this world without perhaps doing what single men do after they've accomplished the majority of what they've set out to do and wouldn't it be, perhaps, the correct thing to try to do something different than his own parents did?
There's just one problem, in looking around, Utsumi's gotten older too. She hasn't gotten married, that's true, but they are definitely not in a relationship where that kind of question comes up naturally. They have trust and she's a logical person, so she'd hear him out. It's a big ask, however.
I think he'd wait for an opening, hoping for it to come up naturally, setting himself a time limit. Or, he'd set about building the relationship he'd think would give him grounds to ask. Because he was given away, he'd not want to adopt, but given how much older Utsumi is now, if he waits too long, that's going to be the only option open to him, with Utsumi.
Utsumi, in having been asked the question, would ask him point blank why he wouldn't adopt. "I don't understand why me, Professor; I thought you weren't the marrying or having children type." He would answer that adopting 'is messy' in those words, and only then would Utsumi get it.
He'd give her all the reasons he's thought out why he wants this, why she would be the person he'd most trust with this, and even suggest that they don't have to be married, they don't have to co-parent, she wouldn't have to be involved beyond bearing the child, and if she's against that? Perhaps a surrogate, whom they would both be responsible for, after giving of genetic material? "Would you think about it?" he asks. She respects him, so she would think about it, seriously.
This Yukawa approaches the whole thing with so much detachment that Utsumi can see right through it. Apart from that one misstep, which is what does the job of focusing her on the underlying emotions in Yukawa, that is. I don't know if she'd fall in with his scientific approach or decide that this is enough to propel their relationship into a closer one. Invisible Helix doesn't give me enough to understand what book!Utsumi would decide to do.
I would like to think, though, that she gently prods Yukawa into examining why he's asking her to ascertain if the question isn't a traumatic response to what happened. She'd want to know this for her own health. It's important. How Yukawa answers will let her know what she needs to do.
This Yukawa takes it all in stride. No fuss; he just wants clear answers. At least, that's what he's projecting. I think if Utsumi told him no, he'd have to re-process his entire worldview concerning their relationship. That might lead to discussions about why she said no, with further re-processing. No matter what, it would make him grow even more.
Oh, and book!Yukawa wants more than one child, a boy and a girl. Being an only child is psychologically difficult; he knows this well. If this all turned out happily, Nae would be very involved in this new project.
Thank you for the question! I was trying to catch a bit more sleep this morning, but this woke me up thoroughly. It was fun to answer!
