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...

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.