Unmei no Hito wa Yome no Imouto Deshita.

is a Japanese light novel series written by Ai Enki, with illustrations by Chihiro Ayaka. The series began publication on July 8, 2022 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
Is it the bride of this world or the younger sister who swore love in the previous life? Marrying without knowing each other's faces - I, Daigo Mido, who had the savagery of being called "blind marriage activity". What appeared at the first meeting place was not a super beautiful bride ... but her younger sister, Shishino. But suddenly, the memories of the previous life come back to us. There, I and Shishino were lovers who vowed their destiny !? ... In other words, the Destined pne wasn't my wife, but her sister !? I'm already married to your sister !? Moreover, in order to protect me from the mess of my parents' house, I started living with Shishino before my wife ...! What will happen to my reason and newlyweds! An unpredictable heroine race that no one has read begins!