Mio has been captured by Zolgia following Maria's betrayal. Basara too is captured by Lars and brought to Zolgia's mansion. Lars' goal is to exchange Basara for Mio. He explains that he's only doing his duty as Mio's observer, but negotiations fail, and Zest slays him.

Basara suffers a deep wound in the battle against the white-masked man after Mio's power. Mio regrets getting Basara involved, and challenges the white-masked man to battle on her own. Meanwhile, in order to protect Mio, Basara resolves to use the "forbbiden art" he sealed away after the events of his past. What was the tragedy that visited the hero village and Basara?

Everyone is trapped inside the body of the demon realm's most dangerous creature, a beast capable of infinitely multiplying until it swallows the entire world. Dimensionally cut off, the only remaining option for Basara and the others is to completely eliminate this dangerous creature's vital core.

Basara goes on a date with Yuki. Unaccustomed to the shopping center, when the two of them are overwhelmed by a clerk's sales talk, Mio stops following to rescue them.

Ten days pass since the battle with Takashi and others. Although the battle ended with reconciliation, Yuki returned to the hero's village. ...or she was supposed to, but when Basara returns home, he finds Yuki in an apron!

Basara leads Mio to higher peaks as he pursues pleasure with the use of syrup. With their master-servant pact reaching a new level, they both bring their full might to face the ones trying to eliminate Mio: Takashi and Kurumi.

Basara and Yuki begin the ceremony to form their pact. Clad in a bustier and garter belt, Yuki was raring to go for it, but she refused to forge the pact normally, and suffered the same succubus curse as Mio.

As the clash between the peaceful faction and the present demon lord faction draws near, Basara visits the peaceful faction along with Mio. Though Basara enjoys their reunion with Zest and Shella, Maria seems to be acting odd. In fact, a heavy punishment was awaiting her for her betrayal of the peaceful faction. Basara begs Rukia for her forgiveness, and ends up administering the punishment in her stead... but that punishment was to spank Maria's behind while she was in a state of arousal?!

The group battle between Leohart and Ramsus's forces finally begins. After Mio wins the first match, Maria enters the arena for the next round. Her opponent is Lars. Maria uses her enormous power to face him in close combat, but she fails to overcome the gap in experience and magic power, and gets driven into a corner by Lars' clever attackes. What does Maria pull out in hopes of overturning the battle...? Meanwhile, the demons lay a cowardly trap for Kurumi.

Ramsus is out to extract the "Demon Lord's Power" that Mio possesses, and Basara reveals his anger at Ramsus' lack of concern for Mio's safety. Just as sparks are about to fly, Shella interrupts them. She leads Basara into the bath to try and help calm him down, and when Zest appears, she orders Zest to massage and wash Basara's body with her bountiful bosom. Then Shella tries to get Basara and Zest to forge a master-servant pact...

The day of the sports festival is finally here. Though Basara remains cautious of the mysterious enemy who manipulates people with magic, he happily enjoys the sports festival with Mio and Yuki as the three of them compete in the four-legged-race and enjoy their youth getting entangled and sweaty with each other. Meanwhile, Kurumi, who was placed in charge of guarding the school, discovers a suspicious individual. At almost the same time, a giant twister forms on the sports field. Basara fights to protect the students... but an unexpected individual appears!

Basara and the others recieve a message from Lars, calling them to Leohart's royal castle. Then Basara's father, Toujou Jin, appears before them all. He brought with him another message from Leohart. A message saying that they　would hold a tournament before Leohart and Ramsus' forces to determine authority of the demon realm--authority of the demon realm being synonymous with Mio's power. After being selected as the representatives, Basara begins　learning "how to win" from Jin.

After ending the battle against Zolgia, Basara regains his peaceful life with his two little sisters, Mio, the daughter of the previous demon lord, and Maria, her little sister who's also a succubus. As Basara pursues the preparations for the sports festival at school, one day he's attacked by a person being manipulated by magic. Recalling the strange gaze he felt at school, a suspicion of his begins to grow...

Thanks to his father's sudden remarriage, Toujou Basara finds himself with two beautiful new step-sisters. Their names are Naruse Mio and Maria. Mio wakes him up in the morning, while Maria stands in the kitchen wearing a suggestive outfit...