One day, Guest was conquering a dungeon in another world with his familiar, the Queen Succubus Eri, to collect resources.

However, as they reached the middle floors, they were suddenly attacked by a female knight.

The person identified herself as Hakua, a Holy Knight serving the interventionist god Fionberg of the Light Faction. She branded the succubus and Guest as evil-doers of the Dark Faction and attacked without listening to a word.

However, Guest is the First Apostle of Rem, the Goddess of the Harem. He is far stronger than the Heroes or Demon Kings of this world. He easily repelled and neutralized the lone Holy Knight with his bare hands.

After being defeated so easily, Hakua immediately turned into a coward, desperately begging for her life. She was the type to be arrogant toward the weak but pathetic before the strong.

Disgusted by Hakua's miserable attitude, Eri performed Succubus Magic, embedding a Succubus Core directly into Hakua's soul.

With her soul turned into a succubus, Hakua's body begins to transform from human to succubus...

The goal is to make Hakua, who views succubi as absolute evil, fall into one herself and learn her place.