
Yeah they well could be siblings, they literally look like the male and female version of each other. At first i thought its coz artist was bored to draw them very different but now even i feel like they could be siblings in a way. We never got to know their relationship from the past life, we also saw what mc thought was true.

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Yes, she looks like his bio mom who passed away early. He never met his mom, but only has that picture of her's. He is currently and in the past TL was trying to throw off his step mom. His step mom is trying to take him off the way of succession to his father's fortune and make her bio son inherit it. So he acts like he using Haesol to replace his bio mom in his life by dating her and giving her preferrential treatment. He even once dresses her same as his bio mom in the pic he has. However when Jaechan asks Woojin later on why would he date Haesol in the past TL, Woojin tells him that he would likely have asked Haesol for a fake relationship to make his step mom let her guard down which will help him attack her when she isn't paying him any serious attention.
Haesol and Woojin look related