Washio Sumi wa Yuusha de Aru - Chapter 3: Nogi Sonoko

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

She, a modern hidden ghost leader of an organization which gathered insane prodigies proficient in the various differing skill-sets. Highly skilled in medicine and poison, executes covert assassinations, viewed as insane and demonic in the eyes of people of the world. Killed in an accident, and reborn into the body of a disfigured young girl.

What? Face disfigured, identity stolen? A return to the family dim and hopeless? Her identity can be given up, her family can be forgone, but as for the one who harmed her predecessor who inhabited this same body, if she didn’t at least make them scream in unimaginable agony and throw them into a state of wretchedness, how could she live up to her demonic reputation? Endless turmoil ensues and it’s a battle to dominate over all! See how she shook the world dressed in a suit of red, her sword up against the dominant powers that rocked the Heavens! Her name spread across the seas, shocking the earth!

- Description from Novelupdates

The empire encompassed endless twinkling stars, but in this dark and terrifying distant future, there were only endless wars.......Gu Hang became the governor of a wasteland planet, where previous governors had all been executed for failing to deliver the tithe on time.Monsters and Low Energy Storms rampaged, survivor factions schemed against each other, technological regression, low productivity, the resurgence of Evil Gods, Green Skin Orcs taking root and sprouting...“Don't panic just yet, let me check the panel below.”[Military Tokens], [Heroes], [Technology], [Events]...Starting as the planetary governor, he would build fleets that traversed the Star Sea, suppressing all alien forms, heretics, traitors, and demons of chaos!Although I formed battle groups on my own, funded Battle Nuns, diverted the imperial tax, and disregarded deployment orders... I knew I was fiercely loyal!Traitors? This is clearly the Third Empire!

All I ever wanted was for famous detectives like Sherlock Holmes or Arsène Lupin to appear in my dreams and share their wisdom. But instead, why am I hearing the voices of notorious serial killers in my head, guiding me to solve a string of mysterious cases?