Song of Sorrow and Estrangement

The beloved human exchange student of the Royal Academy of Diavolo falls into a path of despair.

They've become a demon to save their timeline. To save the ones they loved, but they failed. Instead, they are sent to the past by them as their timeline collapses, being the one who is saved instead.

Overwhelmed by grief, the demon is slowly being torn apart piece by piece. Agonizingly slow and seemingly eternal. Grief that is caused by the loss of everything. Their home, their loved ones, especially THEM.

Familiar faces are here and there, making their heartache so greatly as they remember. The bonds they once shared with each other, are now nonexistent. The joys and the sorrows. The small and big things they've known about each and every one. It's pointless now, as it was nonexistent the day the timeline collapsed.

The familiar face of a crimson demon came. The Devildom's prince. He's found a demon lurking nearby the castle, taking them with him. Now he took them under his wing, and here behold the name he had bestowed them, "Acherost".