What is the Echoing?

“Just as an echo created by a sound gets weaker by every repetition, the Echo of a persona also languishes with every Echoing. It has never been about immortality, only new chances equally doomed to end.” – Maeve Dupont

The Echoing (o Ecoar) is the name of the ressurection proccess some of the more obstinate personas and with greater willpower go through, and when the ones who do it are called Echoes. It is uncertain what makes someone fit to the Echoing, but researches everywhere seek to discover the secret of this immortality.