All of a sudden, strange things are happening in the world, which has been peaceful for so long. Rain, the main character of the story, sets off from Season Castle to find the Hero's Sword, which has been stolen. With him are Cobalt, a Weapon Fairy, and Viola.
They don't know that this is the start of a vast adventure across immense spans of time...
The legends have been passed down.

The legend of how, around 300 years in the past,
the Overlord was suddenly born on the surface of the earth,
and how, using the demons, his kith and kin,
he shut away the world in a chaos of darkness,
inflicting sadness and hardship on humans.

And also, the legend of a single hero who, leading the Soldier Tribe
and the Sorcerer Tribe, fought against the Overlord.
The hero gave his life to bring light back to the world.

The hero's descendants built a new Kingdom
along with the survivors, and worked to
protect the peace of the world over the following 300 years...

With the Hero's Sword, the defeater of the Overlord...