Time had passed, an the tumultuous and tense early days and months began to fade into a new rythm of societal progress. It was not just Arendelle anymore, who turned the once horrible sin of incest into a virtue that every family couldn't live without. It was scary at first, of course. The nations around Arendelle were shocked, and why wouldn't they be? The grandest of nations suddenly brought low to utter degeneracy? At first, the scales of fate moved to snuff out the frosted candle Elsa was creating, but slowly the supposed righteousness of their enemies cause began to fade.
There were many kings and dukes in their anti-incestuous coalition. These rulers, like any other, participated in carnally having their way with their families. It was all top secret of course, known only by the very family members who took part in it. After all, many alliances would shatter to pieces if heirs born from marriages were actually revealed to be be inbred affairs between a princess and her father. So these family love affairs, with queens and princes, to kings and princesses were not a small amount. And over the years the many interlocking family trees and their secrets grew.
And so, as their supposed outrage grew louder and their people feverous for justice, the kings and duke became vulnerable to the very sin they publicly condemned but privately craved. Termed "The Royal Revelation", and almost as if the divine intervened in holy support of incest, the secrets of these many dynasties were revealed. Lords, Vassals, and all. In an instant, their just cause was just no longer. These rulers were now criminals. If, they did not change their laws themselves. Elsa, realizing at last opportunity had come. Not only to solidify Incest as a creed within her people, but to cement the tenets of Incest, Inbreeding and her ideal family structure into humanity itself. As critical to human society as property and stability.
Rushing communications to these fearful rulers, she offered full military support on the condition that they adopt the exact same law as Arendelle, allowing complete familial unity as a sexual aspect of society. Realizing the law appealed to them personally, and preferring the crown rather than their nations principles, they readily agreed. Quickly, the vast Arendelle military became the saviors of these realms, and soon enough the people could do nothing as the supposed degenerate empire became the close ally of their rulers.
Now, 15 years later, society across all the land adapted as they always do. Most peoples of the different nations acted similar to the early days of Arendelle. Shocked and confused, the purely paternal families were forced to comprehend each other as more than just family. But as lovers, and husbands and wives. It was slow, but now forever impossible to undo. And now, none batted an eye when a father fell in love with his daughter, or siblings marrying when they were both young.
And now, Elsa and Anna, the famous and nationally cherished sibling couple that changed the course of history, had two twins. One Boy, and a Futanari girl. History certainly echoed.
Siegfried and Lyla were the two now 15 year old siblings. And being in the family they were in, they were raised within the tradition of the illustrious Arendelle royal family. The two siblings grew up close, and were now; emoitionaly and physically, inseparable. Almost as if the two sisters swapped places, Lyla had Elsa's looks, and Siegfried had Anna's fire red hair.