My Destiny Is the Bride's Little Sister.

Synopsis

I, Daigo Midou, decided to marry someone without ever seeing their face—that is to say, blind marriage. The first person that came to meet me after we got married was my beautiful wife—not. It was her sister, Shishino. And it was at that moment that our memories from the past world returned. In that world, Shishino and I were lovers who had pledged our fates to each other?! So basically, my "fated partner" isn't my wife but her sister?! I've already married the other sister, though?! On top of that, in order to protect Shishino from her family situation, I'm now living with her before living with my actual wife...! What in the world is going to happen to both my reasoning and my newlywed life?! A never-seen-before, unpredictable heroine race begins! (Source: Kadokawa, translated)