Konyakusha wa, Watashi no Imouto ni Koi wo Suru

Aah, again? My fiancé was gazing intently at my charming younger sister. When I saw the blaze that lit up in those cold eyes, I was assaulted by déjà vu. My fiancé had been in love with my younger sister even in the last life. There was nothing I could do but watch. And, by some karma, I was someone who kept returning to that exact moment.

(Source: Shousetsuka ni Narou, translated)