Okay this maybe be a spoiler but they are not actually siblings if that makes you feel at ease. She’s the kid from the family that the Langarage are at war with. She’s the original male leads sister. So it’s not gonna be a incest with any of them even if they do grow up together. I don’t know if she actually even sees them as siblings since she’s not from that world either, I think she sees them as unfortunate children nothing more.
Here's a spoiler
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In chapter 1, Anissa said that she isn't dietrich's sister right? Right. So she knows that she's not a lagrange
It will also be revealed that even dietrich knows that they're not blood related. He already suspected that they're not siblings before but he confirms it from the old traitor guy who used to be a euclid
Tl;dr: both of them don't really see each other as siblings since they both already know that they're not blood related at all. They just need to talk it out lol
But still they grew up thinking the other one thought of them as a sibling, Dietrich especially I mean Anisha literally said they were family. He should've been convinced she saw him as nothing more than a brother. So if neither party acknowledges to the other that they don't see them in a sibling way then it's just up in the air and just some uncomfortable issue to deal with later. Just think if, I grew up with my brother and then when we r older our parents tell us he's actually adopted. Are you just gonna stop seeing him as your brother? No u have lived like half of ur life seeing him as family so it's just gonna stay that way. Just cause they aren't blood related the sentiments alone should make it incest.
I'm not fighting you but I think it would be best not to connect real life with this story by saying "If I grew up with my brother etc etc" esp with a story with this scenario lol and if you really do feel uncomfortable with the story's setting then I would also advice you to stop reading this bc there would be more scenes with sibling love and romantic love that would also probably make you feel uncomfortable
I personally like this story so... But I can understand why you feel weird about it and I respect your opinion about the story
MF I WOULD BE EXPECTING A WHOLESOME BROTHER AND SISTER RELATIONSHIP BETWEEN THEM SINCE THE TITLE LITERALLY SAYS "THE PRECIOUS SISTER" BUT I WAS WRONGGGG I CAN'T HAVE GOOD WHOLESOME SHIT IN HERE. IT'S ALWAYS GOTTA BE INCEST