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.

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.

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...

After taking Kurumi hostage, Ornis robs Basara of the right arm wielding Bynhildr. Though he lost conciousness from the pain, his sealed power unleashes and goes on a rampage. Their positions are reversed as he corners Ornis with his overwhelming power. However, the moment he tries to silence Ornis for good, a golden chain appears and binds him. When Ornis turns around, he finds Hasegawa Chisato. What secrets has she kept hidden?

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.