Emperor's Stand-in: My physique improves a little bit every day

Emperor Daning became possessed and needed to remain in seclusion for three years to heal his wounds. Lu Changjing, who traveled through time, became his substitute and had three palaces, six courtyards and seventy-two concubines.
However, Eunuch Cao was watching closely and threatened Lu Changjing that he could only observe but not use the items, otherwise he would kill him without mercy.
Fortunately, when I traveled through time, I merged with a special object and gained an immortal demonic body, and my physical fitness can be improved a little bit every day.
Taking the physique of an ordinary person as one point, Lu Changjing can increase the physique of an ordinary person every day.
Physical fitness determines lifespan, defense and endurance, and can affect strength, speed, reaction, spirit... and even talent!
The immortal demon body has various characteristics and can be constantly awakened and upgraded, such as: strengthening the body, hiding one's tracks, having deep roots, being able to see in all directions at night, and being able to live forever... until it is reborn through a drop of blood, has the power of Pangu, transcends time and space, and becomes immortal!
Three years later, Emperor Daning came out of seclusion and was surprised to find that all the civil and military officials in the court, the three palaces and six courtyards, the seventy-two concubines, the huge empire... had become the shape of Lu Changjing.