In the Original Soul Reaver Storyline, Raziel was to have gained the Possession ability from its owner the Priestess in the Undercity and Temple deleted areas. The ability would have enabled him to fire a projectile that would allow him to temporarily take control of an enemy character (except bosses), during the time he was possessing another creature, Raziel would have been protected by a shield. It was likely he would have used it to proceed to the next area he would have visited - Turel's Clan Territory.
The possession ability is part of a long line of possession-style abilities seen in the series. It seems to have developed from the Control Mind and Spirit Wrack abilities seen in Blood Omen: Legacy of Kain(and to a certain extent Demonic Possession) It was followed in subsequent games by the Charm and Possession (Defiance) abilities. A further mind control ability which caused damage called Dominate Mind would be seen in use by the Zephonim Deceivers in Nosgoth.
Possession seems to be present in Soul Reaver 2, but it is likely this was a hangover from Soul Reaver and was not intended as an ability in Soul Reaver 2.
It is speculated, that in a similar fashion to Control Mind and Spirit Wrack, the shield that was to have protected Raziel may have been a version of Repel.
It is possible to transfer the camera behind a vampire by using a Soul Reaver trainer. Sometimes it will trigger an unexepected fight.