
Great. Same way that a step anything could just fit a role without truly being/acting/feeling like whatever.
No arguing that she sees him as the "originals" step brother and probable killer.
If it really bothers you, the should be some other manga that follows the "becoming just siblings path". None comes to mind right now.
On this one the spoilers suggest they are the end game couple.

Don’t get so defensive my dude lmao. Was just stating my opinion, incest relationships are disgusting and weird... I mean would you fuck/date your brother or sister..? Even it you are siblings by law it’s weird.. If they somehow stripped the bother and sister relationship they have I wouldn’t mind them becoming a couple as well since they aren’t blood related..

It’s fine lol. Right now I’m reading this
http://www.mangago.zone/read-manga/the_villainess_is_a_marionette/
Female lead and basically her step play her in her last life for some girl, used the Mc a doll and now she has to go back in time before it all started and make sure she doesn’t get stole off again when her brother becomes emperor. The art is great, though only having 20 something chapters I’m already hooked lol. I love how strong the female lead too.
Wait.. is this going to turn into some incest shit? I know they aren’t blood related but.. -I mean they cute but I can’t get past the fact they got a brother x sister relationship.