Usually called "Sannan-san" (based on an alternate reading of his surname), he is also the Vice-commander of the Shinsengumi.
Based on the historical person of the same name.

Source:Wikipedia

The Commander of the Shinsengumi. Based on the historical person of the same name.

Source:Wikipedia

The First Division Captain. Based on the historical person of the same name.

Source:Wikipedia

The leader of the Third Division. He is based on the historical person of the same name.

Source:Wikipedia

Amaimon's title is the "King of the Earth" and another son of Satan.

Source:Wikipedia

A physical form that Amaimon took.

One of the bodyguards hired for Neon Nostrade. She debuts in the 'Yorknew City Arc'. The origin of her name is of French origin, which means 'kiss'.

Source:Wikipedia JP

Sakaki(榊) is a soft-spoken girl who is tall and physically well-endowed. She is also excellent in sports and style. As she is so shy, she seldom speaks, and so her reticence is misinterpreted as being mysterious, or cool.

She is one of the characters with her full name unrevealed and only known as Sakaki.

Source:Wikipedia + Japanese website.

The Classical Studies teacher. In the anime, he is revealed to be the Head of the Sports Festival Committee.

Source:Wikipedia

Commonly called Chiyo-chan.
The 10 year old child prodigy who skipped grades from elementary school and admitted into high school.

Source:Wikipedia