From what I understand from the raw and 3 translated chapters, the family (from many generations) does several rituals during their childhood (ML and MC's) to trap some divine being inside the ML (to bring luck and prospect), the process causes the ML to be sickly and have mood swings. So the MC is adopted and then shoulders the "misfortunes, hurts and sickness" for the ML as a scapegoat. However, the ML obsesses with the MC (even chooses the MC since the younger day), using his power (from the divide being inside) to dream-rape and groom the MC.

Is his brother incubus or something. I regret reading this too early. I miss reading raws on newt'ki