My Sweet Dr. Xu - Chapter 35: Saw His Abdominal Muscles

Sergeant Xia Yao, born into a wealthy and renown ancestry, is a playboy who has turned over a new leaf. Yuan Zong is an ex soldier from the special forces who opened a bodyguard training company after being discharged.

When Yuan Ru, Yuan Zong’s sister fell for Xia Yao’s charms, but could not break down his erected barriers, she came to Yuan Zong for assistance. Little did she know, the moment Yuan Zong saw Xia Yao, this ex-special force knew no other person would ever catch his eye.

And so begins the battle between brother and sister for the most coveted price – Xia Yao’s heart.

- Description from Novelupdates

She, the world's chief doctor of the 21st century, the legendary overlord of the medical world, was killed and her soul transmigrated…She, the useless miss of the Windcloud Empire, was ugly, silly, and obsessed! She died in her own sister and fiancé's hands…When she reopened her eyes again, she had the soul of the strong but the body of the weak…When she became her, her fate would be rewritten and a miracle would appear…This was a story of a two-faced person meeting another two-faced person. With pure hearts, they would end up together.

Amid a world war, with his awakening to powerful special abilities (Soul Armor Abilities), Kamiya Yuusuke, conscripted into the military at the age of 10 due to this newfound power, continued to achieve numerous victories on the challenging battlefield. As a result, at the age of 15, he held the position of Brigadier General.Despite traversing battlefields worldwide, he finally managed to return to Japan. The joy of returning home was short-lived, as news of an underage boy in the military started to leak to the public. In response, the military high command ordered Yuusuke to attend a military school called the Special Operations Soul Armor Academy and undergo a revision of his military records.Yuusuke, secretly pleased at the prospect of reclaiming his youth, faced numerous troubles, whether due to the nature of the unique school or perhaps because he had been in constant battle since childhood. What will happen to his relationships with strong-willed girls such as his half-silver-haired childhood friend, the older sister officer who is his work partner, and the tsundere honor student of the same age?

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