According to Marina Superlatives!, Demyx is the most likely asylum inmate to do nothing of importance.

That said, he habitually keeps up with his sole ambition, to stay on the high score boards of every rhythm game in the Sector 3 arcade.

He yawns off all vague whims to start a Marina band, but has once successfully hosted a Karaoke Party.

He can also be found kicking back on the beach, coaxing the dolphins into song, testing acoustics in the public baths or expending minimal effort to make himself a cup of Easy Mac.

Personality

Of all the nobodies? Demyx would on first impressions strike you as a nice guy to chill with. Frivolous and harmless, friendly, jovial. He's adaptive, and will reflexively treat any non-threatening parties like an old pal. He is very physically demonstrative with his emotions, perhaps to the point of being over-emphatic, to assure the world he does retain memories of the heart and true feelings. Although he plays the fool, he's keenly perceptive, good at reconnaissance, and chatting up casual gossip to earn the favor of stronger allies.

The musician prefers buoyant activities like holidays and entertainments, and is a devotee of his instrument to while away the hours and amuse himself rather than to create anything of meaningful artistic merit. Maybe once that was important to him, when he had a heart. Now it's more of a hollow hobby.

The primary flaw being: He is capricious and lackadaisical to the point of being extremely difficult to motivate.

Demyx openly dislikes the rigors of combat, the expectations of work, and will bemoan most duties as out of his league. He has a few dependable evasive strategies up his sleeve for excusing his own failures with a shrug and a 'Gee, oops?'. Courage is not one of his strong points. He's not a team player in the slightest, will ditch you in a flash if trouble arises, and will readily shirk off responsibilities onto the next available chump!

That said, when backed into a corner, he is fully capable of using his showman's harmlessness against you in a quick turnabout.

He's not as sadistic as some of the others, but at the opportune moment he'd throw an ally under the bus to preserve himself. The Nocturne, like his element, is not quite as harmless and hapless as his languid surface reflects, he's just exceptionally lazy. So you'd best not judge by appearances.

Abilities

He can rock your socks off! (Uhhh...If he feels like it)

-Hydrokinesis, via amplified resonance from his Sitar. His powers are significantly weaker without the weapon in-hand and operational, but music he can manipulate his element into advanced forms such as mirror images of himself. He can additionally generate water where there is none by summoning it from nothingness, but it fades into voidspace shortly thereafter.

-Teleportation, via dark corridors, for the quick getaway.