Raising a Fox Spirit in My Home - Chapter 24

After dying in an oddly anticlimactic vending machine accident, Kazuki Ren is reincarnated in the demon realm—not as a hero, not as a villain, but as the only human male student enrolled at the mysterious Academy of Ruin, a school where all the professors are demon lords and all the students are powerful, beautiful she-demons.Ren is told he has one task: survive.But there’s a catch. The Academy’s darkest secret is about to awaken, and Ren holds a hidden power that could either destroy the demon world... or rule it.Now surrounded by seductive demons with hidden motives, eldritch tomes, forbidden dungeons, and twisted exams, Ren must master his ability—or be consumed.Magic, mystery, danger, and temptation await in this dark academia harem fantasy.

A young man dies tragically while trying to stop a robbery—only to awaken in complete darkness, lost between life and death.As his memories return, he discovers that he’s been reincarnated into a new world brimming with magic, Soul Weapons, and mystical powers. Reborn as Ares into a loving family, he quickly realizes that this world is far from peaceful. Armed with an SSS-Rank Trait and a Unique Ability, he faces every challenge head-on as he searches for his purpose in this strange new reality.

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

Nijigen is a freshman and Banri’s friend. He gains his nickname at the tea ceremony club’s welcoming party after declaring his despair of the three-dimensional world and that he would live for the two-dimensional world from then on. His nickname in high school was “Satoutaka”.