Bonding Ritual

When a Celestial transfers from one host to another, the old host dies as the Celestial leaves, and the Celestial enters the new host. They must be in close proximity, and the Celestial should not be outside of a host for any great length of time.
When done right, there is a Bonding Ritual where the person who is next to accept a celestial (the "Near'bond") prepares their mind and body for the pairing through a series of meditation, dietry, physical, and mental rituals. These can take weeks if not months.
It is common knowledge that most humanoid creatures are suitable for bonding, however due to the history between Celestials and Daemons , any pairing with a Daemonkin is forbiddin, and noted so in the Celestial Tomb.