For me it's less about them being siblings but not biological, but the fact that he treated her so poorly in the past life. I know it's the past life but if he had the mindset to do it before, he could do it again. It's like Hari has forgotten what they did to her and that trauma. Also, it's not like Eugene likes her for her personality, but the fact that's she's pretty, devoted to him, and practically easy to control. Wish she stuck with that other guy, the blue haired one, oh well.