How Demyx joined the Tourney
On an unknown world, Demyx's original persona became a Heartless, his strong will allowing his body to continue on as his Nobody, Demyx. He was later found by an unknown member and became the ninth member of Organization XIII.
Demyx is present when Xion joins the Organization. Axel and Roxas often tease Demyx behind his back whilst eating sea-salt ice cream at Station Plaza after missions, quoting how he doesn't have talent, would be "upset" if he lost his sitar, and many other things. Demyx is the first to mention the annihilation of Organization members at Castle Oblivion. Demyx accompanies Roxas on several missions, including one to Olympus Coliseum, where they take down a Flare Note, and one to Halloween Town, where they tackle a Dual Blade. Demyx enjoys picking on Xion with Xigbar, and is seen playing his sitar on one of the couches in the Grey Area before many of Roxas's missions. When Roxas approaches Demyx, he willingly admits that he "isn't cut out for combat" and would rather perform recon. He is shocked to learn of Xion's true nature when Xemnas describes the Replica Program to the Organization.
Demyx appears alongside Xemnas, Saïx, Xigbar, Luxord, and Xaldin at Hollow Bastion, and laughs emptily with the rest of the group at Xemnas's empty humor at Sora's expense. Upon the Organization's return from Hollow Bastion, he suggests to let Sora carry out his adventures and that they will take action at the right time. This causes Xigbar to interpret his plan as voluntary and forces this plan upon Demyx instead, despite his plea that they have the "wrong guy" before being lectured by Xaldin for acting as though he has true emotions.
On Xigbar's suggestion, he is sent to the Olympus Coliseum in order to find Sora and "liberate his true disposition", either to keep Sora on the path Organization XIII wish him to take, or try to awaken Roxas. Demyx contacts Hades for his assistance, but no deal was made and Demyx promptly flees, saying "Run, run away!", passing by Sora and company, and leaving them puzzled at his outburst. Later, Demyx steals the Olympus Stone, and encounters Sora, Goofy, and Donald within the Underworld once more. Although Sora doesn't understand the meaning of Demyx's objectives nor why Demyx calls him Roxas, Demyx took the next ordered step, which is to attack Sora. However, he is unsuccessful in defeating him and escapes, leaving behind the Olympus Stone. Before Demyx takes his leave, though, he begs "Roxas" to come back to the Organization, leaving Sora even more confused. He briefly returns to explain the nature of the Absent Silhouettes, remarking that by defeating the corresponding enemies, Roxas will "awaken" inside Sora.
Later, during the Battle of the 1000 Heartless at Hollow Bastion, Demyx returns to obstruct Sora, despite greeting him in a rather friendly manner. Although Sora and his friends respond by dismissing Demyx as a threat, the Nobody warns them not to judge by appearances, and his carefree air vanishes completely when Sora remarks that Nobodies lack hearts. Although he attacks the "traitor" with all his strength, he is defeated in the end and fatally wounded. As he laments his loss, he fades into darkness.
Years after, Demyx is restored unexpectedly by Zaheer. Demyx is ordered to convert the Air Nomads to Nobodies, and soon spots a young airbending boy named Meelo.
Character Select Screen Appearance
Demyx plays soft notes on his Sitar Arpeggio.
After the announcer calls his name
Demyx plays loud notes that make water clones of himself as the camera zooms then says "I could reeeally use a break."
Bubble Blaster (Neutral)
Rapidly shoots bubbles at the enemy.
Water Dash (Side)
Dashes forward leaving pillars of water behind saying "Like it?" and ending with a circle of pillars around him.
Geyser Rhapsody (Up)
Demyx jumps into the air while playing a loud note that erupts a water geyser below him.
Form Summon (Down)
Demyx summons two water forms looking like him to fight for fifteen seconds. Needs a recharge after the attack.
Wave Gigs (Hyper Smash)
Demyx readies Arpeggio saying "What'd I do?!" then begins to play his sitar. During the Hyper Smash, a gauge appears with buttons for the attack. By pressing the B or A button in time to Demyx's strumming, Demyx will unleash columns of water that deal water damage to enemies. Meanwhile, Demyx's movement speed is reduced to a slow march. This stops after twenty seconds.
Water Finish (Final Smash)
After yelling, "Come on, keep to the beat!", Demyx strikes the opponent with his Sitar a couple times, sending out pillars, and then ending with a blast of many pillars.
- Demyx spins while playing loud Arpeggio notes then plays a note to send a wave of water out and says "This place is so much nicer, without the loudmouths."
- Demyx sets Arpeggio down then sits down, raises his arms and says "Well, time for my nap." then lays on Arpeggio like a pillow and snores.
- Demyx summons three water forms of himself, then play their sitars for nine notes then the real Demyx says "So, when's our next day off?"
Water forms into Demyx who takes out Arpeggio and says "Dance, water! Dance!"
- Demyx's rival is Aang's grandson and a Tenzin's third airbending child, Meelo.
- Demyx shares his Japanese voice actor with Kamui Shiro and Simon Belmont.
- Demyx shares his French voice actor with Vladimir A. Makarov, Ryuji, Monstrous Ogre, Jet, Necrodeus, Drapion and Tarrlok.
- Demyx shares his German voice actor with Dark Nebula, Tai Lung, Jorgen Von Strangle, Sung Tse-Ho, Numbuh I and Toiletnator.
- Demyx shares his Arabic voice actor with Whizz, Iron Nick (Chunin Nick Uchiha in Japan), Fuuma, Kay von Wollenbarth, Jake Boyd (Tachiki in Japan), Reptil and Jean Vilain.
- Demyx shares his Mandarin Chinese voice actor with Kazuma Torisuna, Muneshige Tachibana and Subaru Shinjo.