Mononoke

Based on the popular noitaminA anime of the same name, Mononoke is the story of a mysterious medicine seller (Kusuriuri) who traverses cities, villages - and, seemingly, time - on a lone quest through ancient Japan in order to vanquish "mononoke," supernatural entities created when a strong human grudge or desire combines with a type of free-roaming spirit named ayakashi. But his quest is not so simple, as the darkness of humanity is endless and makes figuring out the Form, Truth and Regret of the mononoke - which are prerequisites if he is to be able exorcise them - an incredibly dangerous task which rarely fails to turn up casualties.

Each volume or pair of volumes follows the eponymous arc from the anime:

V.1-2 - Mononoke (Note: this is the adaptation of episodes 9-11 of Ayakashi - Japanese Classic Horror, a supernatural anime in which the medicine seller was first introduced before the arc's success prompted him to receive his own series)
V.3-4 - Mononoke - Umibouzu
V.5 - Mononoke - Zashiki-Warashi
V.6 - Mononoke - Nue
V.7 - Mononoke - Noppera-bou