Oko (お香 Okō) from Hoozuki no Reisetsu is the chief assistant of Mortal Hell.
"Hoozuki no Reitetsu" translates to "Hoozuki's Coolheadedness." It's written and illustrated by Natsumi Eguchi. The story is a supernatural dark comedy set in the Japanese afterlife and follows the titular character, Hoozuki, a demon ogre who works as the right-hand man to the King of Hell, Enma.
Oko is one of the many characters in this series. She is a demon who works in the Animal Hell, specifically responsible for dealing with the issues of deceased pets and the like. She is depicted as caring and gentle, a contrast to some of the more fearsome denizens of Hell. She has an appearance that includes aspects typical of a traditional Japanese oni (demon), like horns, but she's often seen with a kind and soft expression, befitting her role in taking care of animals' souls.
Her character plays a part in showing the diverse range of demons in the afterlife and contributes to the exploration of the series' themes, such as bureaucracy in the underworld and the everyday lives of its supernatural creatures.