Majo Ruka is the younger twin sister and long-time rival of Majo Rika, both originating from the same rose in the Witch Queen's garden as candidates for future queenship. Their bitter rivalry, fueled by childhood pranks and sabotage, escalated after Rika won ownership of the Maho-do shop in Misora City.

Ruka first appears after seizing the Maho-do deed from Dela, who won it from Rika. She revamps the shop with chic, magic-infused items that initially attract customers but cause severe side effects due to her use of dark magic. Her assistants are a bat and rat transformed into humanoid forms. When outraged customers destroy the shop demanding refunds, Ruka's crystal ball gets discarded into a dumpster. After protagonists retrieve it, she tricks them into returning it but breaks her promise to undo the curses. Defeated in a magical duel, she loses the shop and retreats to a beach.

There, idol Onpu Segawa witnesses her using forbidden magic, triggering her transformation into a witch frog. Ruka becomes Onpu's mentor, intending to exploit her fame for profit and revenge against Rika. She trains Onpu in magic and the Witch World's language. However, she shows concern when Onpu overuses forbidden magic, risking eternal sleep, indicating a shift from her earlier purely selfish motives.

Following Onpu's integration into Rika's apprentice group, Ruka reconciles with her sister. They transition from rivals to companions, frequently socializing as drinking buddies and confidantes. In later years, Ruka returns to the Witch World and assists in raising Hana after the young witch rejects Rika's care. During a drunken episode, she inadvertently reveals Rika's whereabouts to Hana, confirming their twin relationship.

Ruka possesses a playful yet volatile personality. She is generally easy-going and high-spirited, showing kindness to those she favors, like Onpu or customers. However, she exhibits a foul temper and abusive behavior toward subordinates, particularly her fairy Hehe. Self-serving and competitive, she prioritizes self-advancement over others, especially rivals like Rika. Despite this, she proves a skilled teacher, imparting practical magical knowledge more effectively than Rika initially did.

Physically, Ruka has mauve hair styled in conical buns with gold and black accessories, fair-tan skin, pointed ears, teal eyeshadow, and dark red lipstick. Her typical attire is a black witch outfit with a purple-lined cape, burgundy collar, gloves, shoes, and a crystal ball necklace. As a witch frog, she sports dull green skin but retains the crystal ball. Her wand features distinctive bat wings. She harbors a dislike for butterflies and "old man" jokes.