Apocalypse Alice - a shounen manga written by Japanese light novel writer Takaya Kagami; it's a story about a young man named Shinnosuke Arisu attending a school that specializes in teaches the student to kill girls infected with the labyrinth disease. The reason he is attending this school is to earn money, fame, and power, but his main goal is to save his sister, who is infected with the disease as well. The labyrinths summoned by the infected girls are categorized by ranks from 0 to 666, the highest being labeled as Apocalypse Alice based on the family name of the diseased girl, Saki Arisu, Shinnosuke's younger sister. The people who enter these labyrinths use specialized magic gear and form up in groups to kill the infected girls with less casualties than expected, but sometimes it ends up being more deaths than need be. Although this is a more recent production by Takaya Kagami, the story still holds on par with his other creations. Would like to see this article created to not only provide details on the story, but to also provide notoriety to it as well.
https://www.baka-tsuki.org/project/index.php?title=Mokushiroku_Arisu