Ritsuko Usaka is a girl who has been blamed for various unexplained incidents in Amanogawa High due to her tendency to isolate herself and have certain psychic powers, much like Tomoko. She gives into the persecution and becomes the bad girl everyone perceives her to be as she forms her own witches' coven called the Lunar Witches (月世界の魔女) with other scorned social outcasts.
She is given a Zodiarts Switch that allows her to transform into the Altar Zodiarts, granting her powerful telekinetic powers via her Aradia staff. However, Ritsuko's passion for the occult evolves her Zodiarts form to also use pyrokinetic powers. Creating moon pendants for her followers to wear, Ritsuko uses her powers to make it appear that she and the members of her group are actually witches before Kengo exposes the deception. By then, using the Zodiarts Switch in its Last One state, the Altar Zodiarts proceeds to enact her plan to burn the entire school to the ground.
When her plan is ruined, she becomes infuriated and overpowers Kamen Rider Fourze in battle. Upon transforming into Fire States, Kamen Rider Fourze absorbs her fire-based attacks before destroying her Zodiarts form with the Rider Exploding Shoot.
She returns later on during the Coma incident, where she once considered taking Gentaro to the dance, but the Rider's questioning hurt her feelings and declined the thought. She was later seen with Ryusei Sakuta, who went with her under a threat from Tomoko.