Luxi's been into BDSM for literally the entire comic, what on earth are y'all saying lol. It's the whole reason she goes along with Tongtong's "blackmail," because she enjoyed getting bossed around by a hot girl.
well yes but i hope you'd agree there's a gap between "the characters in this manga are really three dimensional and one of Luxi's traits is being into bdsm, which is why she hooks into this yuri plot that is otherwise not bdsm related" to "our characters are going to learn together and explore what it means to be in a bdsm relationship while we depict them having kinky gay sex right on the page"
Implying a character is kinky, maybe even showing a little bit of it in an empathetic way if you're really invested in your characters, is pretty common. yuri that's an exploration of bdsm is not. It's internally consistent and good writing but the former is not nearly enough to predict the later, which is why I (and I imagine many others in this thread) are expressing pleased surprise.