Arma is a white Shinigami with feathers. Her only facial features are a bright blue left eye, a small nose, and dark lips covering small, sharp teeth. Her upper torso appears to have an insect-like exoskeleton, and the casing around her body resembles a chrysalis. Her arms are long, extending from the bottom of her torso almost to the ground, and each hand has four fingers.
Ryuzaki later sends a coded message to Kira, stating that he has a Death Note. Tsukuru Mishima breaks into his home and makes Ryuzaki bring out the Death Note, allowing Mishima to see Arma.
When Ryuzaki and Mishima escape gunfire, after it is revealed that Mishima is really Neo Kira, Sho Nanase confronts Mishima at gunpoint for killing her brother. As she is about to kill him, Arma writes Nanase's name in her Death Note. Ryuzaki screams as she dies, turning into dust, and she says that she wanted to save someone important to him.