Yukihiro Hongō ( 本郷ユキヒロ, Hongō Yukihiro) Voiced by: Shizuka Ishikawa A student of the school and Mayumi's classmate, with whom he has a crush. Mayumi Koizumi ( 小泉真由美, Koizumi Mayumi) Voiced by: Ritsuko Kasai Miyuki's younger sister, and a student at the school. She is highly skilled in martial arts, often winning several competitions. Haruka fix and correct their unsatisfactory consequences.

When the doctor's inventions go wrong, as is often the case, Miyuki often helps Dr. Haruka and the pretty nurse of the school's clinic and health center. Miyuki Koizumi ( 小泉みゆき, Koizumi Miyuki) Voiced by: Hōko Kuwashima (Japanese) Andrea Kwan (English) A childhood friend of Dr. Haruka's weight was measured by his saliva detector (an invention which could deduce the height and weight of a person by detecting his saliva, which he created to search the school for a phantom food thief (later found to be a hungry germ) to be 105 kg. Haruka has often tried to express his feelings for Miyuki, but is thwarted by both his shyness and the consequences of his crazy inventions.

Managing a medieval castle-like clinic and health center, Dr. Haruka conjures up unique but crazy inventions meant to help his students and impress Miyuki but which often lead to humorous, funny and very embarrassing situations for the doctor, Miyuki and the students and teachers of his school. Secretly in love with his childhood friend and pretty nurse, Miyuki, Dr. Haruka Nishikikōji ( 錦小路はるか, Nishikikōji Haruka) Voiced by: Kōichi Yamadera (Japanese) Russell Wait (English) An overweight and endearing school doctor who has made it his mission in life to assist his students in any way he can.

Haruka Nishikikōji (left) and Miyuki Koizumi Dr.

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