That’s a good question! Honestly, I feel like their development would be pretty linear even if there’d be moments where they’d mess up. It’s hard to ponder about when I haven’t had enough life experience yet. But, um⁓… They’re one of the few pairings in Ansta I can see staying beside each other forever, even if it’d take them a while to actually confess that to each other in a romantic way, which is what I hope you’re asking me about. I think it’d be harder for Tsumugi than it is for Natsume, because to say you love someone is easier than saying you want to change the entire nature of your relationship, especially because he’d be happy as long as he gets to be beside him, or tell himself that, but I feel like he’d selfishly want more, too, not realizing Natsume feels the same — Natsume probably lives with this little thought in the back of his mind that he’ll always love Tsumugi more than he could ever love him, but he suffers because of this in a far more normal boy way, especially after the war.

I’d like it if they moved out of Seisoukan and got their own apartment. I specifically want an apartment rather than a house. So that’s indulgence on my behalf. Tsumugi would be sooo bare minimals (but with a comfy flair, I think) while Natsume would have a more witchy decor style, haha. You’d be able to tell who decorated what. Even if they retire, though I think they’d be a pretty long-lasting unit, Natsume would stay in the public eye while Tsumugi would continue mostly working behind the scenes due to his desire to be in a “support” role (they all are as magicians, but Tsumugi gets a sense of fulfilment out of it like no other despite Natsume also being the people pleasing type).

When it comes to their relationship itself… I think that s&m thing of theirs would persist since it’s a very vital part of their dynamic. It keeps them sane: makes Natsume feel secure, and Tsumugi feel like he's doing good to keep his word. As time passes, it becomes less under-negotiated. Well, they’re kind of already at that point compared to their high school years. But, I feel there’s a lot they haven’t discussed yet. For example, I don’t think Natsume is really aware of how much Tsumugi enjoys their arrangement (thinking back to when he was like, “Whoaaa! You’ve been so kind lately, I’m glad to see your tough side again!” in Shinsekai… that’s not normal at all).

Uuuum… this isn’t “relationship” and more so miscellaneous, but I like to think about them going to events together, and having rings and everything. It’d be comforting to Tsumugi, who has always dreamed of being happily married, but it also really satisfies Natsume’s possessive side. Previously the closest thing was the romanticism of Tsumugi’s ears having been pierced by him that only exists in my mind but I adore it more than anything. I love piercings not only for their look but because of the act of piercing itself, and just, imagine the scene in my head, I could probably write a piece about it if I wanted because it’s hard for me to describe in just a few words in this answer — but that was an event only he knew of. It boosts his ego to have people know Tsumugi is his with something like that as much as it does to stand beside him with their difference in self-presentation. I like to imagine them bickering at the grocery store. And how Natsume’s cats would take a while to grow to trust Tsumugi and let him near them, but one day Natsume comes home and Tsumugi’s passed out from exhaustion on the sofa with papers in his hand and one of them on his chest and the other at his legs, or something, hehe.

I’d like for Tsumugi to learn to rely on him & for Natsume to be less cryptic when necessary (he can still be for fun!). I’d probably have more interesting things to say if I reread Switch stories, the only one I did recently was Tri-lights⁓… sorry if this wasn’t satisfying at all.