Akujo Kyousei Keikaku

"Hey, Seraphina. When you grow up, don't kill me, okay?" The wizard Arvel meets his end at the hands of his fiancée, Seraphina, who would later become the emperor's mistress and a notorious villainess. However, when he comes to, he finds himself face-to-face with a young Seraphina! Astonishingly, he has returned to the body of his 13-year-old self. Seeing the young and still innocent Seraphina, Arvel decides he will help her become a proper lady and save his own life in the process. To start, he must find a way to prevent the death of his brother, Shou, who was once engaged to Seraphina. However, the situation is far from simple, as he must contend with Seraphina's neglectful family, other men vying for the beautiful Seraphina's attention, and a web of conflicting plots. Given a second chance, can Arvel alter Seraphina's fate and save her from becoming a villainess…!? (Source: Bushiroad, translated)