My Pet Is a Holy Maiden - Chapter 21

In a world where magic rules and human nations fight to survive, a 14-year-old stowaway finds himself thrust onto the frontlines of war. With no allegiance but to his own cold logic, Lugh is forced to navigate battlefields of steel, sorcery, and shadows. What begins as an escape soon becomes something far greater—whether he wills it or not.Gunmage – When spell and steel collide, a new kind of warrior is born.

Born into one of the wealthiest families in the country, Layla Rosenzweig's true identity is taken away at the time of her birth by the mistress of her father. She is forced to live as the illegitimate daughter of the Rosenzweig Family. Everyone treats her no less than an outsider in her own house. “This is mine. That is mine. In fact, everything is mine,” Layla's half-sister told her. Everything that belonged to Layla is given to her half-sister, including her boyfriend. Then, she is forced to marry her ex-boyfriend's ruthless uncle, Lucius De Salvo, the most terrifying man in the country. Lucius De Salvo is known for his ruthless ways to get his work done. His name is enough to terrify people. It is said that he is a man devoid of emotions. He will find pleasure in people's pain and misery. He loves to torment those who come under his radar. But why is he so lovely to Layla? Or is it just a pretense?“Are you ready for the wedding night, Darling?” Lucius asked. “I've desired you for a long time.” “What?” Layla was shocked. “Why would you?” “Because you are Layla Rosenzweig. The woman I like.” With that, he captured her mouth for a passionate kiss.

In novels with a stud there is always a Senior Martial Brother like this:

In the early stages of the novel, his innate talent is high, his cultivation is good, his appearance is handsome, and he has an intelligent, cute younger Martial Sister as a fiancée.

In the middle stages of the novel, he is caught unprepared and defeated by a young disciple (the protagonist) in the sect who’s hardly remarkable at all. From then on, he falls from his godly altar and loses his brilliance. Even his young Martial Sister leaves him for someone else.

In the late stages of the novel, he continues to turn dark, going down the Demonic Path and becoming the major villainous boss. However, the protagonist still ruthlessly defeats him and his soul is eternally sealed.

Once Qin Mo opened his eyes, he discovered that he had become this Senior Martial Brother.

- Description from Novelupdates

For the sake of the world, the Protagonist must die.“I... I think I like--”Whether you’re just a girl who fell in love with the wrong person.“N-no...! If I can go back... just one more time...!”A man who regresses to save the world.“Hero... Please, kill yourself.”Or a destined Hero chosen by the Goddess Herself to kill the Demon Lord.No matter what your purpose is, no matter who you are.Even if the whole world and everyone close turns against me...[The target, ‘■■, the Hero’, has been dispatched.][Contract complete.]...The Protagonist cannot be allowed to live.