[The so-called "immortal" is awakened from the sleep of death and returns to the world again with his decaying body.
This is the historical record of the "undead" when they first appeared.
Now they have their own empire, and the emperor who calls himself the "King of Tyranny" rules these resurrected creatures.
From the original unconscious body, an ugly zombie that rotted beyond recognition, to the "undead" that now has self-awareness and can even use magic and martial arts as before.
That transformation only took one year.