Angel had actually wanted to ask this question for a long time.
Borrowing a shell to be reborn was possession. It existed in the Wizarding World as well. For example, Grak, the "Little Demon" of the Edge of the Dark Night, had borrowed the body of someone who had just died and been reborn with Sanders's help. He now went by the alias Spivey and had entered Flora's service.
There was also Gloria, whose original body had been lost in the Nightmare Realm. She had no choice but to find the body of a young girl and temporarily parasitize it with her consciousness.
Both cases counted as borrowing a shell to be reborn, but Grak had completely become another person. Gloria, on the other hand, had not harmed that girl's consciousness; she was merely parasitizing her. Once she recovered her own body, the girl would be able to return to herself.
Although possession existed in the Wizarding World, it was not widespread. The reason was easy enough to understand: possession would only make one weaker; it would not bring any major changes.
The idea of reaching the end of one's lifespan and then gaining new life through possession simply did not exist either. Wizards had all sorts of methods to extend their lives. If even life extension could not prevent death, then it meant that the soul, the sea of consciousness, and the space of thought had all declined to varying degrees.
Possession could not change that either.
Because possession merely seized another person's flesh; it did not alter one's own soul.
Yet the Crystal-Eyed Race's possession seemed to have circumvented this ironclad rule? After possessing someone, they could break through the limit of their lifespan and continue living in a new body?
That was what Angel could not understand.