Vulcan (ウルカヌス Urukanusu) is the eldest of the Jupiter Sisters. Kujou Tsukiyo and her doll Luna are the hosts of this goddess.
Vulcan is fiercely protective of Tsukiyo, she has shown very aggressive behaviour towards Keima and will not hesitate to "punish" him. She sees Tsukiyo as beautiful and innocent. And because of Keima's two-timing, she has a disgust for him.
It is unknown how Vulcan really looks like. When Vulcan is in control of Tsukiyo's body, her hair and eye color becomes into a crimson-red color. She also currently has two wings behind her back.