Akatsuki

Briefly about Akatsuki manga: 

Akatsuki: a potent disease demon that infects victims, causes their eyes to turn crimson, and eventually kills them. They typically manifest as a powerful monster attached to the victim’s body. The only way to heal Akatsuki-infected patients is to cut their bodies with special “Crave” anti-Akatsuki weaponry.

Read Akatsuki manga.

These weapons’ owners and users are referred to as “Kiri-Isha” (Slash Doctors). The main character of this tale, Hibiki, is a Kiri-isha. He is partnered with another Kiri-Isha named Kirisa. Their objective is to treat Akatsuki patients.