User blog comment:B214/Talk About What You Want! 2/@comment-24098614-20140918012609/@comment-1359322-20140918014014

You think the clan would be happy if their clan head is known as a concubine throughout the world. For starters, if they are heiress then it means the husband they would marry would become a part of their clan once married like how Issei has to adopt the Gremory name eventually. So there's no way a heiress can become a concubine nor will the heiress' clan allow it to happen.