I understand your view but they didn't had father and daughter relationship for even a second. And everyone in plot seem to be very well aware about gaslighting and toxicity of their relationship. Author isn't just sliping it in but kind of presenting it for what it is. Wrong. But it's just my view :3
Relationship simply means the connection you have to another person. Legally they are “father” & daughter. We also see him join the relationship with her mother, with the intention of being a “father” figure. Yes the author has made the other characters see the toxicity of the relationship but the romanticization of it is still there. We see this with the sexual scenes that have nothing to do with the plot and the somewhat perception of the women from a male gaze. Imo that is the only thing holding back the manhwa from being a “psychological” story.
It’s interesting but they deff didn’t have to do a father and daughter plot line. It would’ve been different if they were portraying it in a way that was actually trying to show the immorality behind it, but it just seems like they’re romanticizing it