Once in a millennium, when all the elements of the universe are aligned, the Millennium Gate emerges and releases powerful cosmic energy in the form of mythical beasts, sacred weapons and spells. This is an opportunity to harness this cosmic energy to win the prolonged war between two powerful forces:  The "Virtuous" and "Sinners". 
Rise up from around the world are the most powerful heroes from both spectrums. They travel to the dangerous "Shadow Realm" to claim the power and to keep it from falling into the enemy’s hands. Whoever shall claim the Millennium Gate shall win the war, The Millennium War.