Xion (シオン, Shion) is a new member introduced in Kingdom Hearts 358/2 Days. The character's Japanese and English voice actors are Risa Uchida and Alyson Stoner. Xion was first shown in trailers for the new game and has also made brief appearances in demonstrations. She was first believed to have been Naminé, but Nomura later informed the press that it was a different character.
Being the only non-Nobody member of the group, Xion is actually an imperfect Replica of Sora created from his memories by Vexen at Castle Oblivion, on Xemnas's orders to use Marluxia's scheme to their benefit. As such, she is able to use a Keyblade. She was part of an intended series of Replicas (her name being an anagram of her initial designation number, "No.i," based on the imaginary unit), though this series ultimately went unrealized. However, as Sora's memories are the basis of her being, Xion became more than just a puppet as she developed a mind of her own. As a result, Xion's form is perceived by others different from the hooded doll she originally appeared as: Resembling Kairi in the eyes of both Roxas and Naminé, along with Axel and Riku after a while, and Ven to Xemnas and Xigbar. But once she removes her hood, Xion's actual form is that of Sora.
During her time with the Organization, Xion befriends Roxas and Axel, who helped her out while she lost her ability to use the Keyblade. However, while tracking down Riku and losing to him at Beast's Castle, Xion eventually questions the nature of existence as she experiences more memory relapses in conjunction with Naminé restoring Sora's memories. After learning of her origins in Castle Oblivion, Xion resolves to leaves the Organization with Riku's help. After being captured by Axel, Xion learns that Sora's memories are making her stronger while weakening Roxas. Managing to escape during a mission with Axel and Xigbar, after Xemnas deceived her and Roxas in almost killing each other, she meets Naminé as she tells her that giving back Sora's memories would not only destroy her but also all memory of her existence as well. However, Axel followed Xion to DiZ's hideout and takes her back to the Castle, where Xemnas proceeds to reprogram her into his slave after Roxas runs off. Under the control of Xemnas and using the devices scattered across the worlds to increase her powers, Xion approaches Roxas in Twilight Town and attacks him, forcing Roxas to fight back by threatening to absorb him so she can become the "real Sora". After a grueling battle, Roxas defeats her, and Xion returns to her senses. Xion tells Roxas that she is glad that they were friends and pleads with him to stop Xemnas and free Kingdom Hearts before dying peacefully in Roxas's arms, crystallizing completely as her Keyblade passed on to Roxas and became Oblivion.
Due to her being a Replica and not a true Nobody, she was not counted in the Organization as a member, keeping the Organization's number at XIII instead of XIV. Furthermore, though erased from everyone's memories, some hint of Xion resides in the memories of Riku and Roxas. After Roxas loses consciousness against Riku, Xion assures him that she now exists through both him and Sora while promising that their time together will never be truly forgotten. Xion makes a cameo appearance at the end of Kingdom Hearts Birth by Sleep with Roxas and Axel, the three of them eating sea salt ice cream at the Station Tower in Twllight Town, then speaking Sora's name while looking at the sun.