She is voiced by Maaya Uchida in the anime. In the English Dub, she is voiced by Margaret McDonald.
Rikka Takanashi is a "chūnibyō patient" who enrolls in the same high school as Yuuta Togashi. Unlike Yuuta, she still suffers from the eighth grader syndrome. She believes she is a sorceress possessed by the "Tyrant's Eye" that will reveal destinies. She wears a medical eyepatch over her right eye to seal her "Tyrant's Eye". Those who have seen her "Tyrant's Eye" are considered as completely signing a contract with her. She lives with Yuuta's family with her older sister and a fellow classmate.
Rikka and Tōka lived together with their parents when they were young. Everything was fine until their father died. After his death, Rikka went to live with her grandparents. She had some hard times when living with them because her grandfather was strict and did not approve of Rikka's chūnibyō behavior. Rikka still cannot accept the fact that her father died, because it was too sudden. She believes that she can see her father again beyond the "Ethereal Horizon", and is trying hard to retrieve him. She moved to her sister's apartment until she and her sister were adopted wlby Yuuta's mother and father.
Rikka was described as having black hair and black eyes in the novel, yet in the anime her hair was drawn as a dark purple-blue with cyan colored eyes and wears a yellow color contact lens on her right eye, over which she wears a medical eyepatch. She often wears a pair of roller shoes, which she uses in order to increase mobility. Her ahoge occasionally reacts to her mood, in a comedic matter, sometimes moving with sound effects.
Rikka is a classic case of a chuunibyo, constantly living out her fantasies and exhibiting strange behaviors as a result. She is very dramatic and theatrical, claiming to possess the "Tyrant's Eye" which allows her to reveal destines, even wearing an eye-patch to "seal its powers". Her delusions tend to reflect her feelings in real life, such as how she professed that tomatoes burn away your mana so as to avoid eating. Though she does her best to commit to her fantasies, there are a few moments when Rikka will break character, such as when getting flustered or getting hit in the head by Yuuta or her sister. She is alienated by her classmates due to her weird outbursts, and doesn't try too hard to make friends. Though she acts like a cool and mysterious sorceress, Rikka is in fact extremely clumsy, and failed miserably when she tried to join other clubs such as cheerleading.
Later, when Yuuta lashes out at Rikka for using her delusions as an excuse to run away from her problems, she becomes much more somber and mellow. It is revealed that when Rikka's father passed away, the suddenness of his death was so shocking that Rikka refused to accept it, instead inventing a fantasy world which would allow her to see her father beyond the "Ethereal Horizon". With the help of Yuuta, she eventually comes to terms with his death and tearfully says her goodbyes. She reverts back to her chuunibyou state, though this time at peace as she begins developing feelings for Yuuta.
She often brings her main “weapon” around, which is the Schwarz Sechs Prototype MkII, a spring-loaded umbrella. With it, she can cast special attacks such as "Gungnir", "Schwarz Schild", "Wicked Twinkle", "Dark Matter Blaze", "Judgement Lucifer", "Laplace-Sphere", etc.