Konyaku Haki sareta Akuratsu Omega wa Gikei Koushaku ni Shuuchaku sareru

Julius, an omega, is praised in high society as the "Onyx of the Kingdom," but he's disliked for his bad behavior and has his engagement broken off. However, after regaining memories of his past life as a Japanese accountant named Isezaki, he becomes devoted, supporting his brother-in-law, Duke Raphael, in his work and taking care of a beastman baby. Then, little by little, changes begin to appear within Raphael's heart, which was supposed to be as cold as ice...

(Source: Ichijinsha, machine translated)