Brunhild the King's Sister

It has been a century since anyone in the Siegfried clan was born with the Power of God. Desperate to keep their grip on the crown, the royal family resorts to sending its scions to a clandestine laboratory once they turn eight in hopes the brutal experiments conducted there will awaken the children to the family’s latent abilities. When it comes time for Sigurd, first in line for the throne, to undergo the procedures, there is but one thing on his mind: He must manifest the Power of God to spare his five-year-old sister Brunhild the same fate. Though Sigurd triumphantly returns three years later, bearing unprecedented command over the Power of God, the kind brother Brunhild knew is gone, replaced by a violent boy who has forgotten his own identity. Eventually, Sigurd grows tired of Brunhild and banishes her, only to call her back to the royal palace when she awakens to divine abilities of her own. Now betrothed to her brother, Brunhild must find a way to placate the unstable prince if she is to have any chance of surviving…

[From Yen Press]