Apparently, from what I read, the author does him dirty by making him a lunatic siscon. Instead of going for a "love-starved brother becomes protective and loving in a cute way", he straight out killed the MC's nanny just because he was jealous...People (including me) think the author messed up his character for 2 reasons:
- to make the MC the emperor instead of him (and he ended up being exiled)
- to make the ML "shine" in comparison with him as in make the ML the MC's support and develop the romance. The author favored that over developing the familial link between the MC and her brother.
It's so bad, in my opinion and kinda lazy writing in the way that the brother was made to look so bad to make the ML look so good...