Saionji Raki

An android created by Professor Saionji. Raki is supposed to be Amane's sister, but her real purpose is to act as a bodyguard. Because her first priority is defending others, she doesn't always look out for herself -- a tendency that worries Kazuya to no end. Raki can also activate her built-in arsenal by switching to "battle mode" and fight Evolutions along with Kazuya.

(from Hirameki)