After his reincarnation from another world, Setsu leads a new life as a high school student. However, for an unknown reason, he is summoned back to the same world, Eclair. Before he can enjoy his return, he becomes embroiled in the war with the demons that he had originally ended. Though his old comrades rush to his aid, he also notices his old friend's magic on the battlefield. What is going on in the world of Eclair that Setsu enters for the second time?"

Setsu sets off for the demonic continent - and into a chance meeting with the granddaughter of a certain merchant he met once in his previous life, who has her own duty to fulfill...

Setsu, Ruri, and Levia arrive on the demonic continent. They reconnect with old acquaintances and are swept up in a sinister plot involving the Demon Lord and a mysterious merchant.

The Demon Lord Dezastol reflects on the previous war and the promise of peace she made to Setsu. Meanwhile, Setsu, Levia, and Vlad rush to rescue her from the unwanted marriage to the mysterious Terran Sneeter.

While Setsu is fighting his battles on the demonic continent, Yuhi trains to become strong enough to stand by his side. With the help of Elka's tough love, she discovers her own unique kind of determination.

Setsu and Levia set off for the Beastmen continent. On their way, they cross paths with Setsu's old friend Alizee and discover she has been battling a mysterious dragon. Together, they unravel the shocking truth.

Arriving at the Beastmen continent, Setsu and Levia meet Shironeko, a fierce fighter. When Shironeko is asked to assassinate Setsu, she agrees for the sake of her ill sister. All is not what it seems, though, and Setsu uncovers a tangled web of deceit.

In the past, Setsu and Toma are transported to the other world for the first time and Setsu convinces Toma that they can end the war. A strange artifact brings all of Toma's darkest desires to the surface with devastating consequences.

Yuhi reaches the demonic continent alongside the kingdom's forces as both sides ready for a fight. With Setsu still missing on his adventures, they face a desperate battle to hold the line until he arrives.

The final battle gets serious with Setsu's arrival. With his friends old and new alongside him, Setsu is certain they can be victorious and save this world for a second time.

After the defeat of the main forces of Toma, he himself appears to end the world, as he has announced.