コレキヨ Korekiyo
(I love his design so much he deserves a backstory. AHEM.)
"Oh. Good morning, traveller. You didn't talk with that strange Guardian Spirit? Good, good. He is paranoic since the new heir was born."
Korekiyo used to be a travelling merchant. To be more specific, a travelling herbalist. Korekiyo is a special kind of herbalist: he used to use oni blood as a medicine, alongside with his herbs. Korekiyo don't hate onis at all, he loves their powers, their nature and their blood.
Korekiyo is one of the few wolves in the pack that knows how to fight against a oni. He carefully kills them, trying to storage their blood in his glass jars. Cremisi thinks that Korekiyo is actually a reincarnation of an oni, as he refers to oni as his "distant cousins".
Korekiyo is very curious about the heir. The news about him made Korekiyo observant towards him, and always ask Cremisi about his son. Korekiyo thinks that he can use Iguro's blood to some kind of medicine, as Iguro has the Lunar Essence and Oni Powers in his blood.
Herbalist 
Herbalist