Tsukasa spent much of his childhood with the rest of the F4 since his mother was always overseas, and his older sister had moved to Los Angeles after her marriage. His mother, in particular, is cold towards him, and wants to control his life for the sake of preserving the family name.
As the extremely hot-blooded, hot-headed and volatile leader of the F4, Tsukasa uses his power to rule over the entire school. He uses an infamous red card and attaches it inside anyone's locker whose made the F4, particularly him, upset. A red card gives the entire student body at Eitoku free rein to bully, prank and humiliate the receiver until they decide to leave the school. However, Tsukushi's declaration of war against the F4, retaliation against the student body and strong will, after receiving the red card, begins to remind Tsukasa of his beloved older sister, Tsubaki. Unbeknownst to him, Tsukasa begins to constantly do things to attempt to impress Tsukushi, like unsuccessfully straightening his curly hair.
Because Tsukasa is used to always getting his way, Tsukasa is, initially, not very good at interacting with Tsukushi. He frequently makes fun of her family's poverty and responds angrily when she refuses to do as he says. He is also be extremely possessive and protective of Tsukushi, and frequently loses his temper when anyone tries to get close to her. As time passes, he slowly begins to mature and develops a greater understanding of how to interact positively with others, a consequence of his relationship with Tsukushi.