This is something I've actually thought about a lot... I'll link a few of my previous asks that were relevant to this at the end, and get into some new info!

SO. I don't actually write "smut" in the traditional way, I use nsfw scenarios either for "humor" or as a backdrop for something else going on in the fic. So this guide will be focusing on the latter... (Ie I'm less interested in just going "here's them fucking" and more about what's going on in their minds. Idk how to write hot smut / pwp. I have tried... I have not succeeded.... mad kudos to the smut ficwriters)

I think there are a lot of themes to explore with them which might be a good place to start. Some potential ideas are "humanity vs doll" (could factor reciprocity / body image / general nudity), vulnerability (letting themselves be human / imperfect), corruption (like how Mika always infers that they're going to go to hell together / Shu being Mika's "mentor"), guilt (for how Shu has treated Mika before / fear of taking advantage of the other one because of their mental state), etc. I'm just rambling here and I actually don't think any of this would make for hot smut LMAO but it's just where my brain goes.....

Okay trying to talk about like. Actual nsfw situations. I think what helps me is just referencing canon when I can. I often use canon to interpret and justify things in a way that makes sense to me. For example, I'll talk about the dragonfruit story. Shu won't eat the dragonfruit because he says it looks like innards, showing he's a picky eater. I don't think Shu would immediately jump for joy at the idea of performing oral on Mika because of something like this. If he won't put dragonfruit in his mouth why would cock be on the menu? However, this was a story that took place a long time ago, due to Shu's character development this could be something he'd approach. Maybe, performing oral on someone is really special to Shu because he sees it as a sacrifice of comfort on his part so that his partner feels good... So you see how this can kind of be bent to go either way depending on how you take the information that exists?

"Would he behave like this? Would he say this? Would he do this?" and then just thinking of times in canon when it happened / implied to happen helps me a bit. Of course I'm not perfect and there's plenty of people who disagree with my character studies lol but I think focusing more on your own interpretation of the characters to keep it to what feels in character to you would work best.

That being said, here's my personal cheat sheet for Valk nsfw situations
1. Shu is at least verbally a prude- can go either way in a fic though for plot reasons (post-astraea) /mental state, or he can be a hypocrite (says one thing, does another. like. what is maintenance...)
2. Mika is a bit of a masochist, he also really likes being praised (though not without good reason otherwise he doesn't trust it) - S/M + degradation + praise are all on the table
3. Maintenance. Again, what is maintenance?!? Up to you :)
4. Shu is weird about thighs / has a preference for a smaller build + more androgynous look - can be fun to play with gender / transgender characters
5. Mika likes eroguro. Shu... respects this. (Shows that Shu is willing to accept the sides of Mika that don't align with his preferences, may be more willing to try weird stuff Mika's into because he loves him <3)
6. Mika doesn't want to get Shu "dirty" - I feel like he might have a hard time expressing desire to Shu in the beginning because he idolizes Shu too much.

There's more but I'm probably missing them. Hope this helps, I feel like I was a bit all over the place here feel free to send a followup if this sparks more discussion :)

https://retrospring.net/@itiaskia/a/112474991531350611 - How would Shu react to Mika being more "freaky" than him

https://retrospring.net/@itiaskia/a/112357070014230261 - shu's prudeness vs mika's preference for the grotesque

https://retrospring.net/@itiaskia/a/112662191090733593 - shu's prudeness in relation to asexuality

https://retrospring.net/@itiaskia/a/112474907641037723 - mika's masochism

// nsfw discussion!

So overall I would say I'm more of a versitile shipper, however depending on what point in their story they're at, I have preferences for how they're portrayed.

I've talked about this a bit here: https://retrospring.net/@itiaskia/a/112356220033366839

But I've also found that because I'm really picky with characterization, instead of having a dynamic I prefer I moreso have one that I "dislike more" when written incorrectly. Or specific types of plots that appear for one dynamic as opposed to the other. It's funny because I usually take issue with whatever character is the uke lmao. I'm not a fan of like, uwu blushy innocent baby/tsundere stuff that happens sometimes when people reaaaaally lean into top/bottom stuff. It isn't just for them, it's happened to like, every ship I've read things for. Like I'm sure it has it's audience and purpose but it's a squick of mine.

I guess the most surprising thing is I actually don't think they do anal often at all because I can't see Shu, someone who was grossed out about the idea of putting food in his body, ever putting his dick or taking one up his ass. Like I feel that would be a huge character development step for him but I think both of them would be more interested in either like, pleasing eachother (either through hand or oral) or doing something mutual like frotting or dry humping. But I suppose that's more on the sexual side of things and not entirely dynamic dependent.

I guess what matters more to me is like, does the dynamic portrayed make sense for whatever development they've had at the time? With post-canon I'd be satisfied with either so long as the buildup makes sense logically.

Honestly I just like to write, and fanfiction is a very specific way of writing. I see fanfic in 3 ways:
1. A love letter to the original
2. A re-write of the original
3. A spinoff of the original.

Mostly I’d say my fanfics fall in category 1. I like the original work so much that I just want to see more of it! I like the characters and the themes and I want to add supplementary text to areas that aren’t as explored.

Category 2 I rarely dip into, this could be the so called “fixit fic” and quite frankly it’s nothing but disrespect for the original. It’s the “the current writing is awful, here’s how I would make it better” of fanfic. To be honest I usually don’t write from a place of contempt and spite. I can’t say I never have, though. One fic comes to mind in particular where a canon plot point made me so mad I had to rewrite it in a way that made sense to me. The other times I’ve written from this place of emotion were because of a distaste for popular headcanons that I just didn’t agree with, so I had to put my own ideas out there. I dunno, I feel like this kind of fic is a slippery slope of negativity, at least when I write it. Funny enough, I actually hate the source material of this fic I’m thinking of. I didn’t when I wrote the fic. I do now, due to repeatedly poor narrative choices. Do I regret writing that fic? Eh. I just don’t think about it.

Category 3 I also rarely dip into and this is where I would classify pretty much all AUs since there’s no relation to canon other than characters and maaaybe some parallel plot points. I actually don’t care much for AUs because I like the established character relationships in-universe. I do like my own AUs but I find I have a really hard time caring or getting into other ppls AUs because I’m so picky.

I think it's pretty likely that Mademoiselle rarely talked during pre ! era Valkyrie, to the point where Nazuna may never have even heard her speak until after the fall of Valkyrie. My personal interpretation is that Mademoiselle as an alter came around earlier in Shu's childhood and then was dormant for a while and really only came out when he truly needed her (which would make sense after the trauma inducing execution by ex fine). I talk more about that specifically in another ask, I'll link it at the end.

I do think most of Nazuna's interactions with Mademoiselle would be in ! era. I recall Shu saying something like he avoids Nazuna in ! era because he doesn't want to be rude to him and he was still mad at Nazuna for leaving. I don't think Nazuna has the same attachment to Mademoiselle as Mika does, since Mika interacted with her a lot more. I think he'd definitely have some discomfort, I can't recall much of Mademoiselle directly speaking to Nazuna but I know she's talked around him before like in Song of the Garbage Dump. I think Nazuna would be a bit uncomfortable with Mademoiselle, mostly because he wouldn't really understand what she was, but he could tell Shu's mental state was not the best. I think over time he would definitely warm up to her.

https://retrospring.net/@itiaskia/a/112498134162053541

The first one that comes to mind is actually one people used to REALLY disagree with me about pre-raison d'être, but now people agree with me (kinda want to talk about it anyways)

The idea was that Shu is someone, for how loud he praises, who has trouble properly defining relationships and is weird about labels. "Partner in art" / "soulmate" / "two hearts beating as one" are things he'd say but he wouldn't really refer to Nazuna or Mika as "my boyfriend". I saw it first in dragonfruit, where Shu would constantly sing praise of Nazuna and then tell the waiter that Nito wasn't his "lover nor child" then proceed to act like they were in a relationship afterwards... I think it's because the word boyfriend has specific connotations that Shu didn't like the implications of. A "boyfriend" is someone who you date immaturely, where there's a connotation that they could be sleeping together as well, it's sort of a childish love. Partner would be more applicable, but that still has the same relationship expectations. However, these labels are only for the convinience of other people to know the nature of their dynamic. I think Shu himself would consider his position with Mika as a "romantic relationship" but in the Shu version of that.

Pre-raison I wrote a fic exploring the idea of Shu just deciding that he and Mika were in a relationship without discussing it with Mika (who is someone who needs to be spoken to directly). Some people I knew... told me they disagreed with this analysis wholeheartedly, that Shu would be incredibly direct etc. So you can imagine my surprise when the opening scene of Raison included Shu just ASSUMING Mika was going to move in with him in France (without asking) and going so far as to actually purchase furniture for him! And Mika is like huh. wuh.

I think them being in a "relationship" would work a similar way. Shu would just decide they're "dating", yet... not explicitly ask / say that they're together. He'll still say stuff like "my partner cannot be anyone other than Kagehira" and the likes, but directly stating it... I think he's still shying away.

The other hc that comes to mind is more of a preference that goes against a popular hc. I've seen a whole lot of talk about asexual Shu because of his discomfort with sex, I've talked about it before but the way I interpret that is more discomfort with his own sexuality as well as that of others, something he's been steering away from because of how it makes him feel. That's just how he reads to me, I know it's def not the most common interpretation. Here's the link to that discussion: https://retrospring.net/@itiaskia/a/112662191090733593

Tbh I don't think it would change much. I think his issues with his body would still be there, as he idealizes an androgynous "doll like" aesthetic and even if he truly were more androgynously built I think he would still be striving for that. Body dysmorphia works in the sort of way where it doesn't quite go away when the goalpost is "reached", instead the goalpost is moved.

I don't think his body type would affect his personality either, though he still would have been probably bullied as a kid for being girly even if he did "look" girly.

On the flipside, if Shu had been afab I do think their behavior could have changed because the bullying for liking girly things would have been slightly different. I do think they could have still been bullied as a child (girl trying to play with the boys, being called stupid and made fun of for misogyny reasons). I think either way, cis or trans in this scenario, their performance would be similar to current day Valkyrie, reclaiming femininity as something that isn't something to be ashamed of and that can be powerful in its own way.

Usually when I change things about characters I like to transpose their backstories / narrative themes. I do tend to re-structure Shu's body issues with cis!girlShu by giving her curves, as a doll is a sexless perfect aesthetic representation of the ideal body. Being tall with curves could give her a complex of not feeling small/pure enough, especially with how bodies like that tend to be sexualized (something she would disapprove of).

Oh my god perfect.

Teasing Shu...

Ideally Shu would like to sleep between the two of them, but he gets overheated easily so he probably has his own bed and gets insanely jealous if Nazuna and Mika are cuddling together. Joins out of jealousy and then gets all hot and sweaty.

I think Shu likes to play classical music CDs while he bathes and I think it'd be funny if the other two swapped them for something like Mika's death metal collection so Shu has to walk out with his towel halfassedly thrown on to change it because he absolutely will not listen to that while he's bathing.

Nazuna and Mika are NOT the best cooks and have set off the smoke alarm before trying to whip something up. They also filled the fridge up with energy drinks. Shu, the coffee/tea drinker, cries.

Shu doesn't know how he's supposed to act around Koppe and talks to him like he could respond. Scolds him for chewing on furniture/outfits/papers. Nazuna thinks it's funny but he's always a little wary of leaving the two of them alone together because he thinks Koppe's more mischevious than Shu can handle.

"Pajamas" for Nazuna a lot of the times are just a tshirt and maybe some long flannel pants / fun shorts if he's feeling up to it. Mika does the same but if it's summer he's just going to be wearing his boxers. Shu on the other hand has full matching sets, which sometimes Nazuna and Mika split top/bottom and it drives Shu nuts because they're supposed to be a "set" not worn separately!

Koppe has a chair that's his favorite to sit on. It's one of those fancy antique one of a kind sorts of chairs. He fills it full of hair. Unfortunately this is also Shu's favorite chair so he sits there with the lint roller and vaccuum and does his best to rid it of hair. (It never fully comes out. Koppe has claimed it)

Mika likes to hum/sing a little when he's doing chores. Nazuna joins in sometimes. They both stop once Shu tries to join in, because Shu always puts too much effort into it and makes it awkward, and it drives Shu nuts.

Sorry for the late response I just saw this x)