It had been a while since Vina wandered into the succubus world. There, a succubus suggested that, for a practical test, they should try to seduce a man who hated succubi. Vina and the succubus went to the man, Vulcan, but he was as stubborn as rumored, shouting about the sadness he had experienced in the past and his hatred for succubi! "A true succubus! Is a being that gives pleasure to humans!" The enraged succubus attacked Vulcan, possessing Vina's body! Will Vulcan be able to withstand Sacu's incredible techniques!? What will become of Yuina's strength test!? To meet the Succubus Queen, they must proceed deeper into the Demon Castle, protected by a barrier… To return to their original world, to release the barrier, the H-rated succubus training of Yuina, the "onii-chan" calling little sister, continues!