"For as long as you know not of love, you cannot defeat me!"
The young demon lord Cain's father was slain by the hero.
The words he left behind about "love" echoing in the young man's ears...
He decides to learn of love, and become the most powerful being of all.

However, searching far and wide throughout the demon lands... he found not a soul could teach him of love.
In search of someone who can teach him, he summons a girl from another world. Her name is Sara.
Suddenly summoned and commanded by the young lord, Sara is not sure how to teach of love.
Likewise, while Cain may have successfully summoned Sara, he is not sure how to learn of love.

Through trial and error, the two attempt to know of love, but...
As time passes Cain becomes impatient and attempts to perform a "ritual of love."
Something detailed in a book that one of his subordinates brought back from the world Sara is from...!?