Say it louder for the people in the back distracted by their phones
It wouldn't have been weird if she didn't call him brother and saw him as a brother not too long ago. stories like this where the main couple grew up as siblings and turn into lovers later it is always a bit weird the first couple of chapters seeing them actually together. We know Lucian likee her in that way but she was only now seeing him in a romantic light.
And the main point in this story setting is that people who adopt girls are meant for arranged marriage soo there no where they are considered siblings
Yeah the thing is in the Korean language: "Oppa" is used to address your blood related brother, your cousins and *drum rolls* every older guy that isn't in the "uncle/grandpa" zone yet + is "close" to her. So yeah. I think the translations reflect that. There was no filial relationship between them. It was the ML's father who wanted to push on FL being treated as his real daughter, but between ML and FL there wasn't any filial relationship that we can all call out to call this "incesty".
And if ML has used "sister" to refer to FL, surprise again, the same thing happens with "Ddongsaeng" who's is refered to your younger siblings and also someone who's younger + you have a close relationship with. So yeah language and translations, not the actual thing.
She was being nice to him bec she wanted to avoid her death and change the plot. It was clear from the start that he was going to fall in love with her and shes going to realise her feelings late. For all of you who are complaining why do you even read this? They are not even distant relatives. Just because two children of different families are living together doesn’t necessarily mean they are brothers and sisters.