Some people say the greek gods were myths, but they're indeed real. Their children grow up to be heroes, some even becoming famous in the mortal world. However, if the gods exist, then so do the monsters and all those ancient beings from eons ago. One of them, a Titan, is eager to strike rise from the depths of Tartarus and get his revenge on the gods. This Titan's son, Yiannis, a fourteen-year-old boy, is just as dissatisfied with the gods. Joining forces with his father, he seeks to recreate the world based on his ideals.

For the last millennia, sentinels and demons have been fighting a war against each other. Millions have died since then. Gil, a young sentinel, and Maria, a pure-blooded vampire, lose their parents to winged sky dragons. Tempestas, a demon with the appearance of a middle-aged man, decides to take them in. Tempestas lets the two live in his home(the demon realm). He trains Gil and Maria after seeing the potential they have. Before he dies, he tells Gil and Maria of his dream, and the two swear they'll make it happen. Gil and Maria then set out to make a world where demons and sentinels can live in peace.