About thirty years prior to the start of Hagure Yuusha no Aesthetica, a number of selected people from Earth were summoned to other worlds with only about half of them being able to return. One of the young people chosen was Akatsuki Ousawa, who was sent to Alayzard to defeat the Dark Lord Garius, which he did, before returning to his original world. Some of the successful chosen ones brought back little trinkets as souvenirs. Akatsuki, on the other hand, went a different route he brought back the defeated Dark Lord's daughter, Miu, who is now posing as his long lost little sister!

Upon returning, Akatsuki and Miu are forced to join a special school called BABEL where they must train to one day master the powers they gained in Alayzard, in hopes that they will one day be able to serve mankind. Will Akatsuki and Miu be able to keep her true identity a secret or will their plan to live peaceful lives together go up in flames?

Honoka Takamiya was perfectly happy with his completely average and normal life. His primary problem in life was the fact that he shared a school with the school's "Princess," Ayaka Kagari. Both girls and boys fawn over her which makes Honoka's life difficult since he rides the same bus as her in the morning and sits next to her in class. What's worse is that if he even idly interacts with her her fan club takes him out back and beats him up!

One day while taking out the trash he looks up to see a school building falling on top of him! He is saved at the very last moment by the very same beautiful girl, Ayaka, that he's never even had a full conversation with. She finally speaks to him, revealing that she's been protecting him in secret, but now that someone is attacking him directly she no longer needs to do it covertly.

It turns out that Ayaka is a fire witch and there are other witches in the world who want to capture Honoka and use him for the power that he possesses inside of him.

The world has become a slaughtering ground for the Crimson Denizens, mysterious beings from a parallel universe who thrive on the life energy of humans. These merciless murderers only leave behind scant remainders of souls called "Torches," which are mere residues that will eventually be destroyed, along with the very fact of the victims' existence from the minds of the living. In an ambitious endeavor to put an end to this invisible, hungry massacre, warriors called Flame Hazes relentlessly fight these monsters.

One fateful day, Yuuji Sakai ceases to be a regular high schooler he becomes trapped in a crevice of time and is suddenly attacked by a Denizen. Coming to his rescue just in the nick of time is a nameless hunter who seems no different from an ordinary young girl except for her blazing eyes and burning crimson hair. However, before Yuuji can learn anything more about his situation, he discovers that he has already been reduced to a Torch merely a scrap of memory waiting to be extinguished.