Sarah and Armel, two teenagers living on an idyllic island, aspire to become X-Peria, soldiers apartment to a company of the Empire of Galion whose role is to fight from the army of the Demon King to the east of the continent. 

Their daily life is punctuated by training, preparing their escape to the outside world.

However, their dream is brutally interrupted when armed men attack the island, decimating the population and forcing the survivors to kill each other for their survival. 

At the end of the excruciating ordeal, only Sarah emerges as a survivor, integrating in spite of herself the army group and a slave seal is awarded to him.

Confronted with the loss of Armel her childhood friend, whom she had to be killed against the heart to survive, Sarah hosted by hatred swears to become strong to avenge the inhabitants of her island even if for that she has to plunge into the depths of darkness.

Chapter 15 - Everyone has their own reasons.