Rei and Mirai mysteriously appear in a strange world, where a monster ambushes and separates them. To find her sister, Rei unlocks the power hidden within her and fights back.
The sisters reunite, but Anamnesis, the woman who dragged them into Purgatory, stands in their way. Rei battles Anamnesis, determined to return home. However, she loses control of her new power and slays her own sister.
Rei is overcome by despair and lost in grief when she is confronted by the Demon Twins: Mephis and Pheles. They offer to bestow Revival to Mirai if Rei serves them as their Executor. Rei agrees to the contract, determined to do whatever it takes to save her sister.
Now an Executor, Rei hunts the Specters and Revenants in Purgatory. She discovers that they are the Souls of the dead trying to achieve Revival. This news fills her with guilt as she confronts the fact that she has been killing Souls.
Rei makes allies who fight alongside her: Kokoro, Sen, and Nanana. Each of them have their own missions in Purgatory. Rei's heart is torn as she struggles with her shame.
Rei slowly reaches a breaking point. Her feelings for her allies grow distant...and her tears dry up.
After agreeing to the contract, Rei becomes an Executor for Mephis and Pheles, the Demon Twins. An Executor has two objectives:
The first is to defeat the monsters that wander Purgatory.
The second is to collect the special crystals known as Idea.
To give Mirai a future, Rei becomes an Executor and travels between the real world and Purgatory.
The world where the Souls of the dead roam.
There are many layers in Purgatory, each with its own appearance. Mirai's Soul, now dead, is wandering through Purgatory. Rei goes deeper and deeper into Purgatory to find her sister.
After losing Mirai, her last living family member, this room and her dog Thelema are all that Rei have left. Rei can travel to Purgatory by interacting with the mirror in her room and crossing the crest on her wrist. This is where she prepares to enter Purgatory, and where she can sort the items she has collected.
Humans who make a contract with Demons to gather Idea and hunt the Specters and Revenants that dwell in Purgatory.
Beings summoned by a living person's Idea in Purgatory. The transformation caused by their power is known as Blessing.
The dead that wander Purgatory with no self-consciousness. They look like butterflies.
They have the ability to communicate, but since they have no self-consciousness, talking to them goes nowhere.
When the living die their Souls may fragment, which results in them being reborn with a broken self-consciousness. Unlike other Souls, Specters appear as aberrants based on the manifestations of their Idea. Due to their incomplete Souls, they cannot speak and are very aggressive.
Specters that have completely recovered their self-consciousness. They have halos over their heads.
Unlike regular Specters, these ones are capable of speaking. They focus on obtaining Revival by using an ability known as Soul Drain on other Revenants or on living beings.
The crystallized tears of those who have a self-consciousness in Purgatory.
The Demons desire to collect them all.
When a Soul is brought back to life.
This can occur by fulfilling a contract with the Demons or if a Revenant can absorb enough Souls to become completely whole.
An act done by a Revenant trying to reach Revival. They try to absorb the Souls of other Revenants and even attack people living in the real world.