Satsuriku no Tenshi

A thirteen-year-old girl named Ray wakes up at the bottom of a building with no memory of how she got there. A man named Zack, wrapped in bandages from head to toe, is also present. He asks her to kill him and promises to kill her after helping him escape. Their complex relationship grows as they make mutual promises. The reasons for their confinement and the building's purpose remain unclear. They begin an attempt to escape the sealed structure.