Like his fellow members of the Swimming Club, Tanegashima and Mogana Kikaijima, Yakushima 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 his family split up because they didn't have money. Like his fellow teammates, his dream is to fill an entire pool with money, and spend a whole day swimming in it. Nekomi Nabeshima labels him as the type who never reveals what he is thinking, nor what he wants to do. Though he considers money more important than his friends, he likes his friends more than money. Both he and Tanegashima think of Kikaijima like a daughter, and are prepared to make anyone who tries to lay a finger on her regret it.

(Source: Medaka Box Wiki)