User blog comment:B214/Question and Answers/@comment-50.11.177.49-20130502005857/@comment-9297146-20130511144356

Hahaha this guy, why don't you go ask the author himself? Vol. 14 is the newest chapter you guess is as good as ours. Also, Sirzechs and Grayfia would meet in battle alot, and eventually fell in love, during the civil war with the Old Mao faction. So it's safe to assume that the friction there is due to Grayfia "betraying" her faction to be with Sirzechs. Also just because they are sibling doesn't mean they have to get along, personally my brother and I fucking hate eachother and have several trips to the hospital between us thanks to our disagreements.