MTL - Ascend Another Day - Chapter 46 Willows and flowers clearly explain the cause

A princess's duty is to be beautiful, quiet, not loud, to be seen and not to be heard, which was how Dahlia lived most of her life. Bound by the expectations of her title, she spent years trying to prove to her father that she was more than just a princess and capable of being more than an ornament in his court but each time she never got the chance. Instead, she was forced into a marriage of convenience with the bravest knight in all the kingdom, Reagan Hawthorne.Dahlia thought she would use this marriage to escape the brutal crutches of her father and glide out of her cage but Reagan’s cold disdain was an unexpected prison of its own. While he waged wars on distant lands, she stayed behind, holding his household together and protecting the people he seemed to ignore. But Dahlia carried a dangerous secret. By day, she was the perfect wife. By night, she became the “Black Knight,” a masked vigilante fighting for justice in the shadows.Reagan returned, ready to focus on his personal mission: avenging his father’s death. To him, Dahlia was just another pawn in his plans—a spoiled princess he needed to tolerate. But as cracks began to form in her perfect façade, Reagan couldn’t shake the feeling that there was more to his wife than met the eye.Now, with enemies circling closer and their secrets threatening to collide, Dahlia and Reagan must confront the lies they’ve told themselves and each other. But when masks fall and truths are revealed, will their fragile bond withstand the storm—or will it shatter beyond repair?One wound. One secret. One night that changes everything.

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.

Accompanied by all kinds of crisis and despair, was the arrival of mankind’s first significant superhero.