Dorondororon

Humans are under threat from mysterious monsters called mononoke. Dora Sasaki is unbeatable in a fight, and in order to keep a promise to his deceased mother, he aspires to be an anti-mononoke samurai. However, everything changes when he meets a kind-hearted mononoke named Kusanagi. Welcome to this dark fantasy story of humans and monsters!

(Source: MANGA Plus)

Included one-shots:
Volume 4: Fantasies
Volume 5: Dorondororon (pilot)