Angels of Death

When 13-year-old Rachel Gardner goes to a hospital after apparently witnessing a murder, she wakes up with virtually no memories to find herself on floor B7 of a strange, underground facility, in which each unique floor houses one murderous resident in an environment elaborately tailored to their psychopathies. Rachel survives the resident of floor B7, who was her doctor at the hospital, by escaping to floor B6, where Isaac Foster resides. Remembering more of her life and claiming she deserves to die, Rachel asks Isaac to kill her. However, Isaac wants to kill only people who want to live, so the two form a pact: in exchange for Rachel helping Isaac to escape, Isaac will kill Rachel when they do. They then proceed upward through each floor in an attempt to achieve their respective goals.

Synopsis from Anime News Network