So. Chuni gets isekai'd into a magic world, he's the son of a lost tribe of mages. Accidentally becomes stupidly powerful (in the raws he gains the ability to use Appraise, either him or his sister has something like 60 times the magic power of the other), only, uh, it's a medieval society and they want to keep the bloodline pure by breeding him to his sister.
Which is actually something that happened pretty frequently on Earth, so... good job doing your homework.
I do like the art style, and the pacing is pretty good. Basically, he's the only one not aware that his brocon sister is going to be his fiancee -- because he's been so focused on magic that he ignored everything else?