ハーレムブレイド The Greatest of All Time

Cain is a perverted young boy who is supposed to be a warrior. His ancestors killed an evil demon called Gargantuan. Cain's brother, Abel, wants him to take his role as a warrior seriously, but Cain is more interested in ogling the village ladies.

Things take a different turn when Abel disappears and Cain is visited in his dreams by The Goddess of Time. She tells Cain that Gargantuan has come back and that it's up to him to stop it. What follows as a very long journey for Cain to save the world from Gargantuan and develop a harem of beautiful women, though not necessarily in that order.