Cette série se déroule dans un monde où le rang et la survie sont dictés par des 'comptes', des points que les individus portent tout au long de leur vie. Lorsque votre compte atteint zéro, vous êtes banni dans les terres désolées, devenant un 'Abyssion' sans cervelle. Une jeune fille se lance à la recherche d'un héros légendaire pour sauver sa mère, guidée uniquement par les derniers mots de celle-ci. Son voyage la mène à un compagnon improbable avec un compte incroyablement bas, qui semble être l'antithèse d'un héros.
In the world of Alcia' where rank is determined by "counts" a young girl named Hina scours the land for the fabled Ace-the legendary hero of the Waste War. With only the last words of her missing mother to guide her search' she wanders from town to town until she meets Licht' a clownish masked vagrant with a count of --999. Girl-crazy and unpredictable' he's the exact opposite of a hero...or at least' that's how he appears...
Licht and the gang come face-to-face with the deadly demon of the abyss-a modern-day military weapon of steel unlike anything they've seen before. Trapped by giant, weighty wings of metal and indiscriminate attacks from the sky, the fate of the town rests in the hands of the Ace of Flashing Strikes himself! But just as Licht prepares to subdue the destructive enemy, he's greeted by a familiar face-a black-haired, trigger-happy soldier who's also...an Ace?!
Class is in session! As newly enrolled students of Special Military School #13, the gang must plunder stars in order to become soldiers-a title the perpetually hormonal Rihito couldn't care less about. While juggling studies and military training, Jail and the others begin to look for the meaning behind their mysterious time slip, only to come across the school's disturbing connection to the Aces...
Finally, the Waste War begins! With it, a hero is born...but can Rihito protect his comrades from danger? And will Licht and the others be able to return from the past, bearing the memories of three hundred years of misery?
After being captured, Hina, Lynn, and Pele are greeted by Major Schmerman, looking the same as he had 300 years ago in the past they've just returned from. Will he reveal why he betrayed the students of Class A? And what will become of Licht, crushed in his encounter with Douan... ?
"Rihito. You are my enemy." Appearing before Licht, Tokikaze abducts Hinaand returns to the Abyss. How is he planning to take revenge for the last 300years, and what awaits Hina on the surface?
Licht and the gang escape from the clones of A-class and Pele, the traitorous Ace of Piercing Strikes! But Lynn stays behind, swearing, "I'm bringing you back with me, no matter what...!!"