(my hypothesis) Code is some sort of semi mythical recognition code (hence the name, Code) that allow its possessor to have direct link with the world of C. When the link is active, which is as long as the possessor of Code did not transferred the Code to another person, the owner data and existence are simultaneously secured via some 'secure link' with the World of C. Therefore, if the owner dead, he/she will be revived. Since this make use of some information lock mechanism (thus, to preserve the Code Bearer's existence in both world), the owner's information will not altered and constantly refreshed, making they appeared exactly same with when they first receiving the Code and also provide immunity to Geass (since their data cannot be altered, thus any geass capability, which is manipul