I still can't gripe on the whole Kiruko concept. A dude gets his brain put on a girl's body... he's clearly still himself... but treats all romance like a girl in a manga would down to all the typical romance cliches a mangaka who's never dated has. And has no fear of emasculation whatsoever one would expect a straight kid who didn't have much personal growth would have.
I feel the artist is about to write himself into a corner and needs to pivot hard on the brain transplant concept, or make Hiruko come out of the closet. I thought I was gonna see some entertaining ethical dilemmas, ie Maru outright not buying the whole brain transplant thing, unwittingly gaslighting Kiruko after he got raped in that shitty twist but... at the direction it's going, it seems it will be all get thrown out of the window and Hiruko as a character will basically disappear without any good reason.
You don't go this far into bodyswap stuff without asking yourself "why did I write this" - but I suspect any intention of exploring sexual orientation / identity themes got put under the carpet after he realized his fans in Japan would crucify him if he denied them the Pretty Girl Wish Fulfillment.
I agree, some of those themes that should be at least addressed are bit glossed over. I totally understand why Haruki goes around with his new female porte-manteau name, to represent the confusing state he was left in and honor somehow his sister by still using her name as much as he could. Also that it's simply more convenient to not have to try to explain the whole body-swap thing and look crazy.
"Fine. I have a woman's body, so I'm gonna roll with it for now." But still, when Maru confesses, Haruki tells him who he is. A man.
Which is why I'm a bit ambivalent seeing next Maru keep on calling him 'sis' because it's more convenient. (Just like I'm still puzzled by Haruki's whole deal with his sister. are they related? Is it just filial love, incest thrown all willy-nilly like in many mangas, or romantic love if she's just an older orphan he always looked up to?) I get that it's also more convenient to not have to constantly switch to another name and pronouns when they're in public or private,
I would really like to see Maru call him Haruki when it matters. Otherwise, it really looks like Maru doesn't care about the whole reveal or that he's only adding to Haruki's confusion by acting like if only 'Kiruko' matters, when there's more to it.
But since the ship between Maru and Kiruko seems to still be going strong, I think the author might go with it on that front. Haruki was just a boy after all, that didn't exactly have the time to question his sexuality, maybe even start to have the notion of it, so even if it's not easy to reject heteronormativity without that, I could see him just accept that he loves Maru, no matter who he is, his gender, etc. This is all details that don't have to matter.
I think another good opportunity to resolve this will be if Kiruko ever has the possibility to get another body. If he'll go through with it, or if he's after all fine to accept what happened to him; if he prefers to not have to abandon Kiriko's body and grieve his sister completely.
I think Kiruko will stay as is, since that seems to be where it's headed. There's in essence not much difference between being a man and a woman, no matter the million ways he'll have encountered since the change telling him otherwise,
scarring that reality and divide into him through his abuse, for example. No matter if it was a brutal reminder of the feminine condition, he must know that it was most of all a betrayal from Robin, that would have happened in some capacity whether he wanted to rape someone or not. It didn't happen because of anything Haruki did or because of who he is, no, it's only ever because of the rapist and his scum nature and choices.
Same for much more pallatable matter, like love and purpose, when Haruki has never been more capable than since he went out to live as a merc, tits notwithstanding.
Same for Maru. Even if the details are confusing, he just shrugs everything off. He's aware that he wouldn't have developed feelings if he didn't think Kiruko was a woman at first, but he did now, and either way, he would have loved and be friends with Haruki. It's super divisive but I hope the author will be bold enough to explore again those questions, because it's interesting and exactly like learning that the person you're in love with his trans, and all the questions it brings when most people never had to consider where they stood, how fluid sexuality can be.
"Does it matter? Does it change anything for me? Do I have to change one of my little labels informing people on my attraction to an entire sex, or do I paradoxically not have to since that's the point? Is it even relevant anymore to talk about attraction to everyone else when I only care about them now?"
You're missing the point in love matters if you wonder about 'what' when it's only ever about 'who'.