Kingdom Hearts Chain of Memories
The Replica Program was one of the experiments being carried out in Castle Oblivion. Vexen created twenty replicas as part of his research. While two of these replicas—Riku Replica and No. i—went on to become successful in their own right, the initial twelve were deemed as failures, barely considered to be human at all.
The public purpose of the Program was to find a way to replicate a Keyblade wielder's power by inserting a piece of their memory into a blank replica. A vessel deemed unworthy of the program was instead given Riku's data to create the Riku Replica. Said replica shows the capacity to grow in strength by absorbing other lifeforms.
The Replica Program's progress was severely derailed with the demise of Vexen.
Kingdom Hearts 358/2 Days
With Vexen's demise, the Replica Program is rendered inoperable. The only success to come from it was Xion, the only replica from the program to develop into its own person.
As previously stated, replicas can naturally grow stronger, drain the vitality of others or be given an external power up. Xion unknowingly takes Roxas's energy and uses the Organization XIII Devices to obtain new forms. However, the method in which the replica is fashioned can have unforeseen side-effects. Xion's appearance is somewhat unstable as result of her replica body being crafted imperfectly from Sora's memories. Thus, Xion's appearance differs depending on who sees her.
Kingdom Hearts III
Saïx approaches Even and convinces him to become a Nobody once again. With Vexen's research, the real Organization XIII are able to use six replica bodies for the hearts of their time-traveling members, allowing them to stay anchored in the present time. Wishing to atone, Vexen has Demyx deliver a blank replica to Ienzo in order to provide Roxas with a body separate from Sora. Likewise, once Dark Riku's heart is forced out of his vessel, the now blank replica is used to give Naminé a body.
Vexen also repurposed the original twelve replicas, which had previously been deemed failures, into the Replica Xehanorts, each wielding a weapon of the real Organization XIII. In Scala ad Caelum, the Replica Xehanorts fought Sora, Donald, and Goofy before Xehanort himself confronted the trio.
Kingdom Hearts III Re Mind
While Sora, Donald, and Goofy battle Master Xehanort, the Replica Xehanorts attack the Guardians of Light at the Keyblade Graveyard who are trying to keep Kingdom Hearts sealed. The Replicas manage to trap Lea, Roxas, Xion, Aqua, Terra, Ventus, and Riku in a dark void, leaving a weakened Mickey to fight them. With an incorporeal Sora who time traveled from the future lending aid, Mickey temporarily disperses the replicas and pulls everyone out of the darkness.
Following Master Xehanort's desire to keep the pure light away from the Guardians, the replicas return once more, this time merging into a copy of Armored Xehanort. The Armored Xehanort faces off with Sora, who restored Kairi with the power of waking. Sora and Kairi fight the combined replicas, and they are finished off by a combined attack from all of the Guardians of Light.
Replicas are blank figures akin to mannequins that take the form of whatever heart or data of a heart is placed inside of it. They have the same skills as the individuals used to create them. They also have the unique ability to absorb other individuals; Xion passively absorbed Roxas's powers over time, while Riku Replica killed Zexion and absorbed him on the spot to get enough power to battle the real Riku. Riku Replica was created using data Vexen collected from fighting Riku, while Xemnas used Sora's memories to make Xion, an imperfect replica intended to siphon Roxas's powers. Over time, replicas like the Riku Replica and Xion formed identities, and therefore "hearts", of their own, becoming their own people.
In Kingdom Hearts III, the real Organization XIII re-recruits Vexen to continue the Replica Program. As Vexen explains, these newer replicas become real people once given hearts, unlike previous models, which were more akin to Nobodies.
When an innate replica dies, their body vanishes into oblivion; though their hearts can persist for some time (as Riku Replica lingered in the Dark World for one year), or go dormant inside the safety of another's (as Xion did by sleeping in Roxas' heart). Upon their demise, the replica's body dissolves into their element affinity; Xion crystallized into light, while Riku Replica vanished into darkness. The newer batch of replicas vanish more akin to Nobodies do; though they can be saved from this by extracting the dying heart, which was done to give Naminé the vessel of Dark Riku.
List of Replicas
Notes and references