I've Become an Immortal and You Want Me to Be a Security Guard?

[Reverse travel] + [No system] + [No Holy Mother] + [No heroine] + [Decisive killing] After causing harm to the world of immortals for thousands of years, Wu Tian, the famous demon king of the Immortal Killing World, finally reached perfection and broke through the void and ascended to the Immortal World. However, the demon king's ascension went awry, and his cultivation was completely destroyed under the catastrophe. His remaining soul accidentally traveled to a world where spiritual energy was revived, and was reborn in the body of a little security guard who died suddenly after staying up late...