Archangel Volume 1: Ring of Leviathan

Many years ago, heroes of the mortal realm sacrificed their own life to seal away Leviathan, Demon of Envy, one of Lucifer's five wraiths, and trapped him into The Ring of Leviathan. Someone has stolen the ring and has released Leviathan upon the mortal realm once again. On his heroic quest, Kaos encounters Isabelle, a witch, and Apollo, an immortal being. Kaos will join forces with many distinct characters, ranging from the greatest of sorcerers to the most sinister of assassins. It is up to the mighty forces of the Capital and its Seven Knights to find the ring, and seal Leviathan away for all of eternity.

-Written by Hanamiya Kaizaki (This is a very in depth and complex story, so try your best to understand the plot and don't get too confused haha)