Magic

Lumielle's Light
Light Magic is... not really explained in Umbral Soul: Dark Rebirth... What /is/ known is that Light Magic comes directly from Lumielle, the Goddess of Light. Light Magic is powered by Love and other positive emotions/things; most likely protectiveness, honor, righteous anger, and the desire to protect others. Light Magic is used for protective barriers, boosting stats, and even bolts of divine power. As far as it is explained, Light Magic is it's own element, and cannot conjure fire, water, lightning, or wind. These are their own elemental magics, and are (to my understanding of it) lesser branches of Light Magic, and indirectly connected to Lumielle. Since these elements are largely destructive, they're not as powerful as Light Magic, which draws directly from Lumielle, and is powered by the Light Mage's love and positive aspects.

Ragnarok's Dark Gift
Dark Magic is a source of magical power that can be used in a variety of spells. These spells can take the form of virtually anything. Flinging fire, lightning, wind, or pure bolts of Darkness at your enemies or controlling them like a puppet. Dark Magic can even be used in healing spells.

The one characteristic all of these different applications of Dark Magic is its source. The God of Darkness, Ragnarok. Like Dark Magic's counter, Light Magic, Dark Magic stems from Ragnarok Himself. Like Ragnarok, Dark Magic feeds off negative emotions; primarily rage, pain, and hatred. Any negative emotion can power Dark Magic, however.

Iconic Dark Magic spells found in-game are Dark Bolt and D-Medic from Pandora's repertoire; Puppet Curse and Dreadfire Cannon from Damien's spell list; Dark Lightning from the scholar Markus and Ultima Neboros (Need to spell check that one) from Azrielle the Demon King. Not to mention "Oblivion Sigil" from Lord Ragnarok himself. Gryger also uses Dark Magic to amplify himself through his Berserker rage, as well as "Gatebreaker" and his other skills.

Dark Magic's uses are limited only by the Dark Mage's ingenuity, devotion to Ragnarok, and depth of hatred for the Light.