This dynamic is a direct result of their distinctive family structure. While Yuri is indeed his brother, his role is more akin to a servant to Yonhee, who is the chosen vessel of the family's deity. It is a long-standing family tradition for members to serve the chosen vessel, and Yuri was personally selected by Yonhee for this specific duty.
So does he choose his brother to torment him?
I've read the whole thing, so somewhat more caught up. I think their relationship represents the weird dynamic between the family and the god. In which Yonhee is both revered for his power, but highly controlled and trapped by his role Yonhee is the God and his brother represents the family.
So Yonhee immature and acts out in order get some form of control within his life, and his brother cops a lot of this behaviour. But he's sort of treated like a toddler who's acting out, and not a person with autonomy. Because the family (and by extension, his brother) do not see him as more than a power source.
Which is why when Yonhee and MC's relationship is so challenging. Because MC see's Yonhee as a person, with thoughts feelings and control over his actions. But Yonhee has been taught no matter how he acts, nobody will leave him - as they want to use his power. But MC has no use for his power, and did leave him and has held him accountable for his childish behaviour, despite his love for him. So they need to build communication ~
Only up to chapter 31, could someone I guess spoil me - I don't understand the animosity towards Yuri? And why does he allow Yonhee to treat him like that?m
It's also been a while since I read In the eyes of Sora so maybe there's context there. I'm just impatient, idm spoilers lol.