Neuronist Painkill

Neuronist is an NPC of the Great Tomb of Nazarick. It is a special intelligence investigator in charge of torturing prisoners. It delights in its job and inflicting pain, especially since its favorite food is brains.

Neuronist's appearance is that of a huge grey bloating corpse with tentacles and very long fingers with sharp inch-long nails. Though its race is asexual, Neuronist declared itself to be an "onee-san."

(Source: Overlord Wiki)