Yanagi's Senpai

She is a third-year high school student of Central High School and a member of its student council. Her real name is unknown and she is always referred to as Senpai by her underclassman Yanagi and her friends. She occasionally hangs out with the trio and teaches them how to become a cute high school girl. She is on bad terms with Habara's Senpai and is shown to always be the first one to resort to force. It is later revealed that they were classmates during their third year of grade school with Ikushima's Senpai. It is also hinted that she had something to do with the scar on Karasawa's right arm.