Momiji

Momiji is a handsome and top-notch doctor who specializes in treating "mystery diseases" and is Ramune's master.

One of Momiji's hobbies is to torment people and he's especially strict with Ramune. Due to having no sense of direction, he always has "Pipopo" to accompany him, a mystery pet that he created to guide him in the right direction.

(Source: Dr. Ramune Mysterious Disease Specialist Wiki)