"Creator's Choice of Canon or OC Youkai Characters" might work. Natsume Yuujinchou is definitely a “monster of the week” kind of show. With lots of different sub-groups of youkai, from main characters, the dog pack, youkai from the book of friends, exorcists’s familiars, to random encounters.

I could only add so many requests that simply putting down Youkai seemed easier. Sorry for it being a headache.