Kabe Mukou no Hanazono

The "flower disease" is a deadly disease caused by eerie flowers that invade the human body. Lazuli, a young girl born in a remote area, is separated by a wall between the "inside," where people are protected from the flowers, and the "outside," where people are constantly threatened by the flowers. To find out what happened to her childhood friend who went to the "inside" and never returned, Lazuli ventures into the "inside" to find out what happened...? A dark fantasy romance! (Source: Shogakukan, translated)