Hakubo no Chronicle

The story follows Fusegi, a newbie employee from the Ministry of Health, Labor and Welfare who is assigned to the department to work alongside Yukimura Kai, an 88-year-old vampire detective who still looks 18 due to his immortality. Together, they will investigate a series of murders by the “Ram Killer” that have been occurring every Christmas in the year of the Ram over a period of 70 years.
~~Adapted from the manga series "Hakubo no Chronicle" (白暮のクロニクル ) written by Yuki Masami (ゆうきまさみ)
(Source: Drama-Otaku)