Thousands of years ago, in an era when Muggles and wizards persecuted and hated each other, the only thing that could protect themselves and their companions was useful magic.
Slytherin's current position in the wizarding world is in jeopardy. Although it is still the controller of the upper class, its prospects are getting worse and worse. However, there was a prophecy thousands of years ago that the stars in the east would bring the purest souls, and use the souls as sacrifices to turn the tide.
What happened thousands of years ago that made Salazar Slytherin run away in anger without even leaving a word? What happened thousands of years later to make Salazar Slytherin reappear and not even care to shock the wizarding world?
The purest soul is burdened with the purest darkness, allowing the real Slytherin to reappear from a thousand years ago to a thousand years later; and the sacrifice of the purest soul has become Slytherin's lifelong guilt and regret, and the nightmare continues from a thousand years ago to a thousand years later.
Satheron Slytherin: Not only Salaza Slytherin, but also Godric Gryffindor, even Rowena Ravenclaw, and Helga Hufflepuff, who is not very powerful in attack. They all agreed that no threat can be left that may endanger the wizarding world and the existence of Hogwarts, even if it is a Muggle!