Talk:Karren von Rosewald/@comment-29558690-20170405051948/@comment-10733658-20180614224215

^ Are you an anime-only watcher? Because the manga goes into more detail about Karren's decision.

Because both her brothers died before she reached Japan, she decided that it was her duty to become the Rosewald heir. So she adopted the "Kanae" identity, and introduced herself to the Tsukiyamas as a boy.

Shuu explicitly refers to her as "little boy" in their first meeting, and everyone acts like Kanae is a guy in spite of knowing the truth.

The whole thing is less that Lord Rosewald wanted it, and more Karren internalizing the trauma of being the last survivor. The Tsukiyama/Rosewald clan is pretty traditional, meaning the heir had to be a man. So Karren became Kanae, and tried to "become" the entire family and take the place of the dead brothers.