Nagi Takishima is a beautiful but very strong girl. She's Kei's cousin and is one year younger than him. She is also supposed to be Kei's fiancé, which Kei doesn't agree to.
Nagi first appears when the S.A. go to Akira's villa to celebrate Kei's birthday. While they are there, Nagi shows up. She greets Kei but not the others, then starts to act hostile toward them, especially Hikari. They soon figure out that Nagi is only there for Kei, and is his fiance. This surprises the S.A very much. She then notices how Kei acts towards Hikari and gets very jealous. She starts to complain and act like a spoiled brat. This causes Kei to get very furious with her, and soon causes a problem. Nagi again, starts to complain and to cry because Kei loves Hikari more than her. She soon starts to yell at Hikari and hurt her. Hikari then tells her it's ok and cheers her up, like she always does. This causes Nagi to notice all she wants is Kei to be happy, and is also invited to his party. Nagi then says sorry to everyone in the S.A and gives up her feelings for Kei. Hikari and Nagi reconcile and become friends.
Nagi has a sassy and hostile personality. She wants to get everything she wants when she wants it, but inside, is a loving and caring girl. Nagi loves and cares for Kei even though he doesn't truly love her. Which is why she is a good person inside.