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...

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!

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?