[Short Story Version] An Incompetent Young Lady Goes to Marry the [Demon of the Far East] as a Substitute ~ My Parents Told Me "Die in Your Sister's Place," So I Decided to Leave Home. But Everyone at My Husband's House Is Kind, and I'm Happy.

※I've started serializing this! https://ncode.syosetu.com/n2756ju/ The protagonist, Lei, was born as the eldest daughter of the Saiga family. In a world where magic is everything, Lei alone possesses no magical power, and thus spent her days being oppressed by her family and those around her. One day, by royal decree, her younger sister was to be married to the Ichijo family, an aristocratic clan from the Far East across the sea. However, the place she was to marry into was a magical realm where terrifying demons roamed. Furthermore, the head of the Ichijo family, Ichijo Satoru, had been given the nickname "the Demon of the Far East." A doting father who loves his children decides to send Lei to the Far East in place of his stepdaughter, Ariaru. Lei agrees, seeing it as an escape from her hellish environment, and crosses the sea. "You... have incredible spiritual power. That's amazing." In fact, Lei, who possesses no magical power but tremendous spiritual power instead, becomes deeply adored by Satoru. And it's revealed that Lei is the reincarnation of a great demon, Zashikiwarashi. Her very presence brings prosperity to the household—a power that makes the people of the Far East desperate to have her. Meanwhile, the Saiga family, having lost Lei, finds itself rapidly declining.