Adel Frost is the firstborn son of the Frost family and Edel's older twin brother.
Being male and firstborn, Adel should have been the one to carry on the family tradition by becoming a swordsman and revive the name of his family. However, Adel suffered from a debilitating disease and could not leave his home.
Perhaps unknown to even himself, Adel possessed the strange power to open portals between dimensions. This power attracted Dreyfus de Villepin, who masqueraded as an artist for the family to get closer to Adel and thus use his power to summon demons. His evil plot succeeded, and after opening a portal to Elyos and granting passage to the demon tribe of Arachnids the whole region of île de Frost was affected by a sinister curse. All inhabitants of the island were dominated by demonic spiders, becoming violent creatures of darkness.
Though Edel managed to defeat Countess Arachne, the leader of the demons and close the gate, her brother who had been trapped between the worlds was sucked into the portal and ended up in another dimension. This caused Edel to embark on a journey to find him.
Adel was mentioned within the dialogues of the dungeons from île de Frost.