Monmusu Quest! Origins: Assaulted by the Vamp

In a world where monsters take the forms of women who lust after a substance only men can give them, one boy is fated to change everything forever. And to continuously get raped doing so.
The plot starts when Luka, hero of this story, has a dream of the goddess Ilias who commands him to take up arms, become a hero worthy of her and slay the Monster Lord whose legions of monster girls attack humans everywhere.

[From Mon-musu Quest Wiki]