Thank you for the comment!
Yeah I see Reisen/Kaguya in the Japanese fandom from time to time (though still not as popular as Reisen/Eirin or Kaguya/Mokou) but as far as the the english-speaking fandom goes I've only seen it in a couple of fics, I don't really remember why I started liking it but it's been my favorite Eientei based ship for a while.
I wanted to write Sumireko and Hatate interactions since they have some similar motifs and it ended up being Hatate engaging in a lot of "teenage girl" things that Sumireko thinks she's too good for lol