Seven Gates

After the great battle for power between gods and demons ended with contract which suppressed the demon kind , the demons were always hated by all for being weak and powerless.
Being born in this cruel world a boy, to prove that he is not a demon travels to a gate which is said to kill all demons. What is this gate ? Why does it exist? no one knows
Where the gate leads no one knows for all tho who ever entered the gate were all considered dead.