Also, don’t forget the author has drawn clear parallels between Marcille and the samurai, a man who explicitly stated he wants to marry Farlyn and take her home with him. And the brother clearly disproves of the samurai while it doesn’t seem like he would be against Marcille being with his sister. Also, Marcille is studying magic in order to make sure she never loses people she loves, by extending life spans. In a manga where the main character is both clearly and tastefully written as autistic, I really trust this author.