Errr, what? If you're talking about Ran and Yus they aren't blood-related and became step-siblings only because their parents married each other.
I get that some people have a problem with fictional incest/quasi incest (ie step siblings brought up as real siblings etc) but how is this anything like that? Ran and Yus aren't related, they were never brought up as siblings, Yus was pretty much packed off to boarding school the minute reincarnated Ran entered the scene and they've only interacted with each other as young adults.
But their parents married eventually make them siblings right?... Wouldn't it be odd
Well, i hope it turn out to be that their parents didnt marry pls or maybe fl isnt her mothers daughter