"Androids loaded with synthetic souls, which only SAI has successfully developed."
A Giftia is a type of android with a humanoid body that has been developed by Sion Artificial Intelligence Corporation (abbreviated as SAI Corporation). It is said that Giftias are the most accurate imitation of human life that the world has ever seen, something which no other corporations have accomplished.
Giftias are practically capable of doing anything and are virtually indestructible, but they are given "limiters" so that their functions are kept below a threshold, thus deeming them safe to coexist with humans. They would be indiscernible from humans if not for one crucial aspect of their existence: their lifespan. Giftias can only "live" for a maximum of 81,920 hours (approximately 9 years and 4 months), after which their programming becomes corrupted due to numerous failed attempts at overwriting old information.
If a Giftia is not retrieved and deactivated before the end of their lifespan, it is very likely that they will become "Wanderers". When a Giftia becomes a Wanderer, they act only on instinct, and not on personality nor memories. It is also possible for them to become violent. In order to prevent this, the Terminal Service, a department of the SAI Corporation, attempts to retrieve Giftias before they become Wanderers.
A Giftia who has been retrieved and deactivated cannot regain their personality nor memories, regardless of any attempt at doing so. It is possible, however, for a new operating system to be installed in the Giftia's body. This is similar to being "reborn"; the Giftia's identity and personality will be entirely different from that of the previous operating system installed in it.