So, the current idea I'm toying with is an Isekaied into Royalty!AU.
Here's the premise: So, the Reader insert has been isekaied into a royalty AU based on some novel she read only halfway through in her past life. She, however, has read through all of KNY. So imagine her shock when Nakime and Koyuki are the ones to check on her as her ladies in waiting.
That's right. You're a princess now and to your shock (and disappointment), you are now the daughter of Shinjuro Rengoku. You don't have the standard features of a Rengoku, looking like yourself. But nobody questions it. And if you question it? Well, everyone thinks the princess is having a bit of an episode. Simple as that. And why wouldn't she? You're expected to pick from a lineup of suitors, including your cousins (royalty things).
The first suitor is Sekido, Urami's heir. In the novel you read, he was who you married… you think. See, you're not exactly the main character. Mitsuri Kanroji is and she's engaged to your elder brother, Kyojuro. But enough of that, back to Sekido.
From what you remember, his heart was never yours. So honestly, is he even that good of a match?
Then there's Karaku. You'd think he's a diplomat given that he works with your father a lot and is quite the charmer. Weirdly close with his knight though. Odd. Sanemi Shinazagawa would've hated Karaku's guts in their canon universe, but has fallen for him here.
Aizetsu... exists. He's not really interested in doing the leg work to pursue marrying his second cousin.
His twin brother, Urogi, though? Very interested. Very playful, and does his best to woo you. He does want twelve babies though, so keep that in mind.
The last suitor in your kingdom doesn't formally hold a title. He's a bit of a guru, taking up the mantle of his priest father. Douma is mildly interested in marrying you. He stands to gain a lot from your union, but has no hard feelings should you pick someone else.
Your father's other top pick for your husband is Prince Muzan from a neighboring kingdom. He's attractive and mysterious, but his secrets might be a bit more than you are ready to handle.
Also from the other kingdom are the Tsugikuni twins. Now, from a political standpoint, Michikatsu is obviously the better option. He will inherit a title, land, servants, all the things a princess could want. Sure, he's a little cold, but he is a gentleman. After all, he wasn't raised in a barn like his sweet, titleless spare of a brother, Yoriichi.
There's also a few other options, but none you could openly marry of course. Marrying a peasant is far beneath you… even if they're really dreamy…
Now if only you finished that damn book.