O Debu Akujo ni Tensei Shitara, Naze ka Last Boss Ōji-sama ni Shūchaku sa rete imasu

After dying of illness, she has been reincarnated as Celine, the selfish, fat, villainous duchess, sister of the heroine of a popular novel. If she stays this way, she will be killed by the hero prince and die a miserable death, just as in the novel. She vows to reform herself with all her might and begins to struggle, but she finds herself caught up in unexpected doting and obsession..! Will Celine be able to find "peaceful happiness"?