Demyx

Bakugan Interspace
When Saix wished to charge the form of the Organazation members to their original form, he needed to borrow Hades' pet, Cereberus to cause a distraction to steal the darkness cube from the officers. Hades just wanted an offering from the Organazation in the form of a member. Saix then tricked Demyx into coming with him to the Underworld, trading Demyx's soul to borrow Cereberus for 24 hours. After this betrayl, Demyx spent years in the Underground prison, bitterness and hate growing for Saix, plotting his revenge.

The Narnian Battle of Puzzle
Demyx finally breaks out of prison when a monkey named Puzzle offered him freedom in exchange for him to be Puzzle's bodyguard. Demyx accepted and went with Puzzle to Narnia. While defending Puzzle's Castle, Demyx comes across Jason who tells Demyx to stand down. The two battle, however Demyx was prepared for Jason's electricity. He covers Jason in water to prevent him from using any of his electrical attacks, otherwise he'll shock himself. Demyx eventually knocks Jason down, and holds Jason down by the throat using his sitar.

Death
Jason decides to electrocute himself in order to shock Demyx off of his throat. Jason also summons his Oathkeeper keyblade into his hand. With that he delivers a final blow. Demyx's sitar melts into water, and Demyx fades in darkness.