The Heartbound were once known as Spirits. They were ethereal creatures born from concepts. Being such transcendent creatures, their arrogance grew. They looked down upon the human and oni races, waging wars against them. Tethered by concepts, Spirits would not be stopped by mortal methods, allowing them to commit atrocities uncontested. As a punishment, their creator bound their hearts to the physical world and made them mortal like the others. Throughout the ages, old generations withered and new generations bloomed. However, grudges from all sides continued to grow. The hatred accrued with time until one day, it happened. The day of the incident marked the beginning of a tragedy.  Altair is a Heartbound who lives among humans and oni. Having mixed feelings about his ancestors, he hopes the hatred between the three races will one day dissipate so that a devastating war does not break out. One fateful day his home is attacked by Heartbound. That is when he meets Vega, a mysterious figure who, like him, wishes to prevent a war that has been silently brewing for over a decade. However, Vega seems to have another reason for meeting Altair.