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A young girl named Rachel awakens at the bottom basement level of a closed-up building. She's lost her memories and has no idea why she's here.

Rachel is saved from an attack by Danny, the man calling himself her doctor, when Zack appears. She asks Zack to kill her, and he agrees as the two of them start to search for a way out of the building.

After arriving at the small room in the back of the reference room, Rachel encounters Eddie, the digger of graves and master of Floor B4. Eddie claims that he knows what happened to Rachel's parents and why she's in this building.

The door to Floor B3 opens to reveal a space like a prison cell, enclosed by pure white walls and iron bars. The moment Zack strikes the locked door before them with his scythe, the duo are barraged by machine gun fire.

Rachel finds the key card to get them out of the poison gas room, but Zack handles it too roughly and breaks it. The hourglass announces that their time is up, and a powerful poison gas begins to pour into the room.

After willingly shooting a dangerous drug into his arm so that they could move forward, Zack begins to grow overwhelmed by the urge to kill. But with the last traces of rationality left in his mind, he tells Rachel, "Don't let me kill you just yet..."

After slashing open his own belly, Zack is left without the strength to stand, so Rachel sets off alone into Floor B2 in search of something to stop his bleeding

Rachel heads to Danny's floor with Gray, the priest, to search for something she can use to treat Zack. However, Gray tells her she must undergo a series of tests to get there.

Danny, who Zack thought he killed on Floor B5, shows up and offers Zack a deal: Rachel's eyes in exchange for medicine to treat his wound. Meanwhile, Rachel finds Zack's room on Floor B6 and retrieves the knife he asked for.

Carrying Zack's knife, Rachel sets off once more, determined to find Danny and get the medicine she needs to stop Zack's bleeding. But once again, pink smoke carries her away into a world where she can't tell illusion from reality.

Gray proclaims himself closer to being a God than anyone else and sentences Rachel to burn alive for the things she did to the other floor masters. Hanging on her cross, Rachel insists that she's not a witch and that she only wants Zack to kill her.

Floor B1 looks like an ordinary residence. After following a trail of blood to what appears to be a living room, Rachel suddenly panics. She pressures Zack to kill her immediately, then passes out. Then Danny appears, only to shut Zack out of the room and tell him, "If you succeed in learning everything, I'll open the door." So Zack sets off to search the floor on his own for the truth...

As Zack is looking around in Rachel's room, a TV suddenly turns on and starts playing a news story about a bizarre murder case.

Zach confronts Rachel after learning the secrets of her past.

Zack and Rachel have found the stairway leading to the building's exit. At last, the end of their ordeal is in sight... but as they're climbing the stairs, suddenly an alarm sounds.

Zack struggles to get Rachel outside the building. But what kind of future awaits her on the outside?