Younger sister of Judy Devens. A young girl that tried to hire Zwei (aka Reiji), thinking he was a killer for justice, by using money she had unknowingly stolen from Inferno. Reiji tries to hide her from Inferno but is unsuccessful and in a move to save her life asks that she becomes his assistant.

She appears two years after the death of Ein, when Master is finally making his move. It is hinted that Ein was the assassin that killed Judy and so crossed the girl's faith with the cursed faith of the name Phantom assassins.
After an attempt on his life, Reiji took her for dead and was forced to leave America to go into hiding. Cal believed that she had been left behind by Reiji and was manipulated by an exonerated Scythe, who turned her beliefs into full hatred for Reiji and trained her as his third assassin. As a memento of her grudge, she continues to hold onto the pocket watch that Reiji got for her.
She is destined to become Scythe's trained assassin known as Drei. Her appearance changes drastically from a small girl into a biker model. She is now known as Phantom, as so once was Zwei after Phantom's and Masters betrayal.
Nearing the finale of the series, she continues to pursue a climax for her hatred and grudge towards Zwei. Zwei attempts to make her stop by offering his life and asking her to leave Elen alone because he doesn't want her involved with Inferno again, but that makes Drei jealous and even angrier, realizing that he wants to protect that women even in death. The two finally confront one another, following her usual game involving the pocket watch. She of course is killed by her superior, Zwei who deeply regrets doing so. Placing the pocket watch in the hands of her corpse, it later saves Zwei from the final phantom, serving as a distraction.
(Source: Wikipedia)