Unbeknownst to the living world, celestial beings oversee their cycles of existence and reincarnation. One human continues to be an exception, with the help of an Angel.
The Human does not bleed, age, or die. They wonder if they are even human at all.
To prevent the living world from getting suspicious, the angels hunt down the Human to erase them from existence. The Angel, in love with the Human, refuses to let go and tries to hide the Human from them.
Whenever the angels find the Human, the Angel kills the Human in order to reincarnate them and shake their pursuers off their trail. Each time the Human reincarnates they lose all memory of their past lives, but even so, the Angel loves them in each one.
The Angel will make sure that the Human lives, even if it means killing them to reincarnate them over and over, trapping the Human in this endless loop.