If you're already of age and an independent adult, no one can force you to treat the *adult* son/daughter of your parent's new lover as a sibling, or not date them. It'd probably be different if the new sibling was underage, but when they're not, you're definitely not forced to treat them as a sibling, and you can date them.
Oh, yeah, it'd definitely make many of the people around them misunderstand and/or feel a bit weird, sure. But once a parent's child becomes of age, an adult, the law recognizes both the parent and their adult son's/daughter's respective right to date and marry without consulting one another.. ┑( ̄Д  ̄)┍
No one should be forced to disclose their personal information to a stranger online for the sake of argument you weirdo. And just because you're an adult, you're not allowed to read these types of stuff anymore? There's 24 hours in a day, you don't work for 24 hours straight in case you didn't know. If you don't like the premise of the story then leave. Get your negative and immature ass out of here and let people enjoy things. Imagine thinking reading something actually equates to you doing it irl. You saying people who read/watch psychological content are psychopaths and murderers too? Grow tf up. And if you can't even bother to actually find out what a word actually means, you might need to work on your vocabulary then, kid.
For the nth time, it's not incest. How hard is it to understand definitions? They're not blood related, therefore it's not taboo. Sure a lot of people might find it weird because you don't see it often, doesn't mean it's wrong. By your standards, maybe. And if we respect that kind of relationship, does it automatically mean we do the same? What kind of narrow-mindedness is that? I, for one, as another example, would not date someone 30 years older than me because I'm not into that or have not at least found myself in that kind of situation yet. But I respect people who do have that kind of relationship, as long as it doesn't involve minors that can't legally consent yet, despite most people finding it weird. Just because I don't think there's anything wrong with step siblings dating who are more than old enough to decide for themselves and are not even living with their parents anymore, doesn't mean I do it, too. I'm not promoting it but I'm not judging either. Stop acting like keyboard sjw's in a fictional story ffs. Just say it isn't your cup of tea and move on with your life. No one needs you preaching here.
Smh not step bros.. welp this is gonna be incest