Like his fellow members of the Swimming Club, Umumichi Yakushima and Mogana Kikaijima, Tanegashima is obsessed with money, and is willing to go so far as to risk his own life to get a hold of it. Kikaijima claims this attitude originated after the orphanage he grew up in foreclosed due to lack of funds. Like his fellow teammates, his dream is to fill an entire pool with money, and spend a whole day swimming in it. Though he considers money more important than his friends, he likes his friends more than money. Both he and Yakushima think of Kikaijima like a daughter, and are prepared to make anyone who tries to lay a finger on her regret it.
Tanegashima has tan skin and blond hair. He wears red swim trunks and a pair of white arm bands. Tanegashima has pointed teeth, giving him something of a shark-like appearance. When not in the water, he wears the standard men's uniform of Hakoniwa Academy. At the Seiyasai, Tanegashima wears a light colored scarf with his uniform.
Because they didn't have money, the orphanage that raised Tanegashima was foreclosed.
Student Council Executive Arc
Tanegashima and the other members of the Swimming Club are first introduced discussing the upcoming club battle swim meet. Tangeshima calls it a retarded event, though Yakushima tells him not to be that way. As a group, they decide that when they win, they will be one step closer to reaching their dream of filling a pool with money. Come Sunday, all three are seen looking pleased when Medaka Kurokami announces that any club that ranks higher than the Student Council will receive money from her own pocket. Tanegashima alleviates Kikaijima's worries about the first event, insisting that in the water, they are better than the beast Medaka.
After the first event ends, the Swimming Club is seen on the sidelines. Medaka points out that they were actually the first group to score all twenty points. Other onlookers discuss the Swimming Club, one claiming he saw the guys swim to the pool's bottom, even with floaters on their arms. Medaka confronts the club, identifying the technique they used as compulsed expiry diving: if they had made a single mistake, they could have drowned. She asks them if they value their lives, a question Tanegashima answers on the rest of the club's behalf: they value money more than their lives.
Yakushima and Tanegashima take part in the second event, the three legged race.  When the race starts, the Swimming Club initially lags behind, due to Yakushima needing twenty-five meters to match Tanegashima's speed. With the preparation complete, Yakushima apologizes to Tanegashima for making him wait, who tells him it's not a problem. The two then begin swimming with their legs tied together, easily reaching the finish line first. After the third event, the Swimming Club confronts the Zenkichi Hitoyoshi and Kouki Akune, Tanegashima reminding them that the Swimming Club's funds will be increased by three times for outscoring the Student Council. When Zenkichi asks him if he could at least pretend to have fun, Tanegashima brushes him off, insisting that money makes the world go round. After Medaka claims that she will reform the Swimming Club, Tanegashima haughtily dares her to go ahead and try.
As the fourth event starts, the cavalry battle, Yakushima and Tanegashima are seen as the horse supporting Kikaijima, with Tanegashima in the back. Tanegashima asks Yakushima what they should do. When Medaka tells the Swimming Club that she will teach them that there is something more important than money, Tanegashima thinks to himself that she better stop talking, as saying there is something more important than money is taboo to Kikaijima. When Kikaijima declares that she will take that "stupid girl" (Medaka) down, Tanegashima has nothing to say. When Medaka knocks Kikaijima off balance and kisses her, Tanegashima is shocked. When Medaka comes out of the water carrying Kikaijima, Tanegashima accuses her of being crazier than they are, and that even if they lost, they are not going to change the way they live their lives. When Kikaijima asks the two of them which is more important, her or money, Tanegashima adamantly insists that money is. When Kikajima goes on to ask which they like more, her or money, he and Yakushima share a look, before both tell her that they like her more. He is shocked with everyone else when Nekomi Nabeshima and the Judo Club are revealed to have won the competition, and thinks that Nabeshima was surprisingly cool about being cheap.
Some point before accepting Medaka's offer to join the Student Council, Kikajima approaches Tanegashima and Yakushima to ask their advice. Tanegashima tells her to join them, as she should learn a little more of the outside world.
Kumagawa Incident Arc
Kurokami Medaka's Successor Arc
Unknown Shiranui Arc
Bouquet Toss To The Future Arc
Tanegashima is among the students who confront Medaka at the beginning of the 100 Flowers Run, holding flower number fifty-three. He and the others are all blown away by Medaka's Kurokami Final. All present wonder if Medaka thinks of their time together as good memories. His message to Medaka is to remain friends with Kikaijima.
Ten years later, Tanegashima and Yakushima continue to swim, now doing so professionally.
Swimming Prowess: Tanegashima is a Special and one of the school's many scholarship students. Tanegashima is Vice-Captain of the Swimming Club; his talent is widely recognized, even outside of the club; in the world of men's swimming, he is considered the fastest.