Shisha Kanrikyoku: BLOOD SERVANT

To save his younger sister, who is destined to die within three years, Kō Saejima joins the Corpse Management Bureau, a job that promises to earn 100 million yen in a single year…
But it turns out to be a monster-extermination workplace where 90% of new recruits die within their first year!

(Source: Cycomics, translated)

Note: Includes one extra chapter.