Nagi Takashima is Kei's cousin and is a year younger than he is. She is a beautiful girl with unbelievable strength. She appears during a brief vacation the SA take at Akira's villa, where they intended to celebrate Kei's coming birthday.
Extremely arrogant and full of pride, Nagi proclaims herself to be Kei's fiancée and loves him very much. However, she quickly becomes jealous of Kei and Hikari's closeness with one another and ends up acting unpleasantly towards the rest of the SA in order to get Kei's attention. Upset that Kei, the only person she feels comfortable around, cares more about Hikari, Nagi tries to get rid of Hikari, who comes to see that Nagi only wants to please someone she cares about. Afterward, the two reconcile and become friends.