In the ancient times gods created three worlds and gates between them separating human world from ghost worlds.
Yagami has no parents and lives with his grandfather. He comes from an ancient demon hunter birth-line who have guarded the gates between the worlds for as long as the world existed. Yagami is one of five guardians of different elements - he is the the master of fire. After meeting one girl his live starts to change rapidly.

[From vndbreview]