On his fifteenth birthday, Yūsuke discovered that he was not truly related to his mother, Akane, and his sister, Rumi. His biological parents were Akane's close friends Haru and Ryōsuke, who were both involved in separate car-related accidents on the day of his birth. His mother died shortly after he and his twin brother Sasuke were born, and his father died to save a child in the street.
Not certain how to handle this new information and the idea that he was utterly without blood relatives, Yūsuke ran away from home and wandered around aimlessly. After meeting Taisuke, who had been the child his father saved, Yūsuke received the present that Ryōsuke had meant to give to Haru after the birth. The letter inside, written to the then-unborn children, talked about how they should help other people. However, angry that his father's mentality had resulted in the man's death, Yūsuke flung down the letters and claimed that he would only live for himself. After watching some upperclassmen bully a student his age, he discovered that he had truly inherited his parents' blood because he couldn't resist stepping in to help (the student was later revealed as Tsubaki) - though he ended up being beaten himself. Later, after having accepted his circumstances, he returned home and continued to live with Akane and Rumi, stating that they are the only family he has ever known.
Appearance
Bossun has messy dark hair that curls upward on either side, above his ears. He is almost always seen wearing a red, horned Poppman cap and goggles. His most common outfit consists of a white shirt with the sleeves rolled up over a blue-and-white shirt of his own design which has the word SKET across the front, blue knee-length shorts, black bands on both ankles, and a pair of sandals. He wears wristbands on both wrists - one with red, white and blue stripes and the other with the Sket Dan symbol on black. Attached to his shirt are several pin buttons. He has a wide range of facial expressions, most notably his "embarrassed" face, where he purses his lips comically.
Personality
Bossun is particularly know for his enthusiasm for helping others, he has a positive mood which makes him very optimistic. He is kind-hearted, and is very righteous. He is also a little wierd, establishing a club that helps students and as stated by Himeko. Bossun will do anything to get the request done and right, even if causes him humiliation and embarrasment.
Concentration Mode: Bossun is able to utilize an extraordinary level of perception when he equips his goggles and mentally recalls relevant facts to the problem at hand. His perceptiveness is so keen that he can even make out distant sounds in the background of a phone call. This level of concentration also makes him an excellent shot with the pachinko ball slingshot he uses as a weapon. After using this ability, he often ends up taking deep breaths like a diver resurfacing.
Artistic Talent: He is, comically, an extraordinary artist - both in 2-dimensional and 3-dimensional form, as evidenced by his stint making origami. His fellow club members have joked that his artistic talent is a strange one for a manga protagonist.
Vocal/Facial Impressions: He is able to do spot-on impressions of various characters and Japanese celebrities, such as comedian Rakutarō Sanyūtei and baseball player Eiji Bandō.
Relationships
Bossun and Hime holding hands!
Hime "Himeko" Onizuka:His relationship with Himeko is complicated - they aren't lovers, but they are undeniably more than friends or very close friends. In 'School Trip Rhapsody' arc, Bossun himself said that he never even thinks about his feeling towards Himeko. In chapter 157-158, when Bossun implied that Himeko is dating Kiri, Bossun is irritated, but continues to show "relief" of sorts. It continues that anytime Himeko acts close to Kiri, he feels annoyed.
Roman Saotome: Roman refers to him as "my prince" and he once saved her from being hit by a truck. She might have a schoolgirl crush on him, though it is not expanded upon much.
Saaya Agata: At first, Saaya treated Bossun just like the other clients of Sket Dan since she just needs the Sket Dan's help. Since Bossun helped her alot, Saaya begin developing romance feelings for him. In 'School Trip Rhapsody' arc, as Switch gave her an advice, Saaya asks Bossun what did he think about Himeko (but at that time Himeko is in Bossun's body). On chapter 167, Saaya finally confessed to Bossun but she is indirectly rejected. He still sees her as a friend, and allows her to go to his clubroom anytime she wants.
Sasuke Tsubaki: From birth, they are twin brothers who were separated and raised by different parents due to Haru's request. They are rivals who always fight anytime anywhere they meet, but they show some brotherly love toward each other. Bossun often helps Sasuke and so does Sasuke even though both of them refuse to admit. They show the same bashful expression whenever they are being equated with their twins.
Trivia
Shinohara states that Bossun's surname is a combination of the character "fuji" (藤) from Fujiko F. Fujio and the character "saki" (崎) from Hayao Miyazaki. His first name comes from the musician Yūsuke Chiba.
Bossun is right-handed and the first kanji of his name (佑) means "right."
