Rumi Fujisaki

Rumi Fujisaki (藤崎 瑠海, Fujisaki Rumi) is Bossun's foster sister. Though she frequently treats him like her personal servant, she also genuinely cares for him. She is first introduced as a middle school student then later attends Kaimei High School from Chapter 210 onwards.

Appearance
She has short brown hair like her mom. Her hair is separated into bangs and each side is clamped by a hair clamp. When Bossun turned 15 and he was still a freshman, she had a shorter banged hair.

In the third opening, she is shown wearing a sailor uniform (possibility her middle school uniform). But in the fourth opening, she is shown wearing a shirt as her uniform.

Personality
Rumi has a slightly arrogant attitude and often makes Bossun buy things (namely food) for her. She does love her brother dearly, however, and worries about him constantly (especially when he turned into an otaku). After Bossun learned about his true biological parents and ran away, Rumi spent all day looking for him. After he came back, she ordered him to buy him a cream-puff for causing so much trouble. Bossun had known beforehand that she would probably ask, and had bought one on the way home, causing her to laugh, cry, and playfully punch him at the same time.

Upon meeting Tsubaki, she acted as if she were a queen and tells him that if he wants to become close to her, he must provide her with sweets. This reminds Tsubaki that he had brought desserts to give to Akane, Bossun and Rumi's mother, as a gift. Rumi makes a similar face to Bossun's "interested/impressed but not wanting to show it face", making Tsubaki think that she and her brother are really quite similar. They get close enough to share phone numbers and Rumi once called for Tsubaki's assistance when Bossun fell victim to an addictive video game.

Eventually she graduates from middle school and goes on to attend Kaimei High School with her brother. She meets the Shinzou brothers for the first time and thinks that the older brother Shinzo Takemitsu is very old and plain looking. In contrast, she thinks the younger brother Shinpei Takemitsu is very handsome and takes an interest in him.

She has a good relationship with other Sket Dan member like with Switch, whom she often texts or asks for updates on Bossun's love life, and Himeko who is like a sister to her (although during their first meeting Rumi thought she was a foreigner).

Rumi even told Switch in Kaimei's school festival that she often worries that if Bossun didn't get a girlfriend, he will fall in love with her because they aren't blood relatives yet are so close.

Etymology

 * The name Rumi means "lapis lazuli, precious stone, gem" (瑠) (ru) and "sea, ocean" (海) (mi).
 * Rumi's surname Fujisaki means "wisteria" (藤) (fuji) and "cape, peninsula" (崎) (saki).