Thank god some people in the comments mentioned his name, and that apparently being the Korean honourific
I was so confused because i thought his surname would be the same as the sister, and then it looked like it wasn't
I mean, we read these translations because, supposedly, we don't know Korean, and this setting isn't even in Korea (or an isekai), so having obscure Korean thrown at me is kinda weird XD
But at least this group doesn't seem to do the annoying "tl notes" gushing over all the characters, so being confused over one person's name isn't anywhere near as jarring