LET ME PERHAPS try to clear up some confusion / misconceptions about this drama!

First and foremost, their childhood:

I think I understand a lot of people's perceptions on how weird their brother/sister relationship was HOWEVER - please note they were CHILDREN and you really have to see it from a different perspective.

I think the love that Joonsuh had for Eunsuh was way more innocent than people think (like they had an amazing sibling relationship, with a lot respect, care, and bondness (or jeong/jung) between each other - in Korean there is a term called "JUNG" or "JEONG"; in English it directly means affection but it's a little more in depth than that.
I know some scenes were odd - like where he talks about how he likes someone blah blah; but I think he just meant to say that to tease her but at the same time genuinely did "love" her or have affection for her as sister. He just really was the overprotective brother.
BUT to each their own - I did think their affection for each other was more so innocent / naive and really didn't start blooming into something unhealthy until right after they were separated.

When they got separated; it sort of built a trauma bond between them (?) They were torn apart and it was just such a heavy blow for both of them. I especially think for Eunsuh - it made her miss not just her brother but her whole family and sort of formed a trauma love around him. Same for him since he had to just adopt a new "sister" back into his life.

Overall, WOULD RECOMMEND!! Such a heart wrenching and loving story. I honestly love Eunsuh - she played such a TRUE main girl as the good hearted/poor character which was the THEME back then.

Give it a shot!! They don't make it like this anymore :')