Replica Riku is a whole bunch of confusing and interesting. He was created as a copy or "replica" of the Real Riku, so that the higher-ranked Nobodies in Castle Oblivion (Vexen, Lexaeus, and Zexion) could try to get a leg up on the younger upstart Nobodies (Marluxia and Larxene) who wanted to use Sora for their own purposes. So, every side wanted their own "pet Keyblade Master" to toy with.
Repliku's memories (which are very very important to him, as everything else he has is "fake") have been broken and remade on numerous occassions, so he's almost hovering on an edge all the time, torn between killing his Real Thing (so that he can be the only "real" Riku), and being sympathetic and kind (since he does have Riku's memories of Destiny Islands). Mostly, Repliku turns Riku's emo and angst into bitchiness and angst, with a good helping of snark.
Also, while he makes light of the "lessons" he learned from Larxene and Vexen (and to a lesser point, Axel), Repliku very much did not enjoy being controlled by the Nobodies. They always treated him as a Nothing, with complete disregard of his own feelings and desires.
Naturally, Repliku comes from the Chain of Memories game version of the events, with the minor change that he didn't "die" in Riku's arms, but instead vanished into the Dark and managed to survive (the way he did in the CoM manga). So now, Repliku is unsure of his place or purpose, and has rather latched on to Riku as something familiar.THINGS THAT INSPIRE HOW REPLIKU IS PLAYED:
--> Intelligent Design
. Vexen closes his eyes and smiles with his teeth because the replica screams just like a real boy.
by JokesterAmsBesides, the two of them were nothing but an imitation and a shadow of a person. Despite the wicked acts the duo had caused, the keyblade master still forgave them.
--> Our Farewell
by Iridescent Hope.I writhed under him, not from the sexual feelings, but from the attention I was getting, the intimate contact that I knew only came to you when you became Someone. But why? Why would Real Thing care about me...
by Absinthian.The replica- who is unaware of being a replica and only knows himself as Riku- plays with the star-shaped charm in his hand, turning it over repeatedly. He smiles. He likes this memory, the one of the night where he made his promise, and she gave him this charm.
--> a real memory
."Like this," she tells Riku, her Riku, the one full of memories she made.
--> Most Wicked of Games
by endling."I'm not weak. I'm not weak like him. Give me another name."
--> Reflections of Oneself
by DarkHybridChild.You wonder when he changed from wanting to kill you, from wanting to be the real you to just being content to being your other half, to be whatever you need him to be.JUST TO FUCK WITH RIKU'S HEAD:
--> Deep Shadows
riku riku riku riku rikurikurikuriku
--> Dance of the Dream Man
.She flushes a bit, glances down. "...Marluxia... Is this right?"
"For him? No."
.Everyone gets spam.
--> A Darkened Heart
.Having had Sora's darkness in his hands is something he needs more of. When Sora drives it away from room after room Riku catches up to it again and wraps it tight in his arms, holds it against his body, breathes in its reek. It dances slightly against him, because that seems to be what it wants to do: dance and play and hurt others.
--> Sora Gets Lucky
.Sora gritted his teeth, prepared. There was no other choice.
He bent over.
by JokesterAms.The two who currently took space within his arms were like precious gems to him. It was up to him and only him to keep them pure. To keep the two protected from harm. To take them far, far away.