Rika is portrayed with dark eyes which appear light brown in the second anime season and dark hair. Kodaka Hasegawa describes her as having a slightly childlike yet strikingly beautiful face, though he often remarks that her eccentric and perverse tendencies contrast sharply with her outward appearance.

In the early volumes of the light novel, Rika commonly wears glasses and ties her hair into a ponytail with a yellow scrunchie. By Volume 4, she reveals that her glasses were fake, explaining that her eyesight is perfect, and she begins wearing her hair loose while still using a scrunchie. Over time, she frequently experiments with her hairstyle, including temporary changes to blonde and black hair in Volume 5 using one of her inventions, before returning to her natural color in Volume 6. In Volume 8, she again darkens her hair during a pivotal confrontation with Kodaka.

Her typical attire consists of the St. Chronica’s Academy uniform, which she often pairs with a lab coat, even in public settings. Occasionally, she adopts alternative styles, such as a one-piece dress in Volume 6 after Kodaka’s remark that she would be more attractive if she dressed elegantly. From Volume 8 onward, she begins appearing in casual clothing within the Neighbor’s Club. Rika also owns a yellow bikini, though she is still noted to wear her lab coat over it.

Rika is characterized by her eccentricity, bluntness, and strong fixation on sexual themes, often making her the most forward member of the Neighbor’s Club. Her introduction highlights this trait, as she openly makes inappropriate remarks toward Kodaka Hasegawa in front of their classmates. She habitually turns ordinary conversations into innuendos, treating such behavior as natural rather than shocking.

A self-proclaimed fujoshi, Rika is deeply immersed in BL (Boys’ Love) media, openly reading yaoi manga and playing related visual novels and games. She frequently fantasizes about pairings between her male peers, particularly Kodaka and Yukimura Kusunoki (prior to Yukimura’s true gender being revealed). Her unusual preferences extend even further, as she humorously expresses arousal at the idea of mechanical beings engaging in intercourse. Rika embraces her own perverseness, claiming it adds dimension to her identity beyond being viewed solely as a scientific genius.

Despite her provocative personality, Rika shows a caring and considerate side, particularly toward the members of the Neighbor’s Club. She is highly attuned to their well-being, often providing support in subtle ways. While she enjoys teasing and surprising her peers especially the usually composed Kodaka she becomes visibly flustered when faced with genuine affection, often blushing intensely when someone acknowledges her sincerely.

Beneath her eccentric front, Rika is among the most dedicated members of the Neighbor’s Club, investing significant effort behind the scenes to ensure that group activities, such as the virtual reality game and film project, are meaningful and enjoyable for everyone. This reflects her earnest desire to achieve the club’s founding goal of building friendships, even when others downplay their bond by claiming they are still “friendless.”

Rika’s quirks also extend to her manner of speech, as she often refers to herself in the third person, further reinforcing her unconventional personality.

Intelligence
Rika is recognized as a prodigy and is widely regarded as the most intellectually gifted character in the series. Her scientific expertise allows her to invent complex gadgets and technological devices, which has led to offers of employment from multiple companies despite her young age. Her exceptional talent was one of the reasons Principal Tenma Kashiwazaki personally recruited her to St. Chronica’s Academy, aiming to enhance the school’s academic reputation.

Physical Prowess
In contrast to her intellectual abilities, Rika’s physical endurance is relatively poor. She becomes fatigued easily, struggling with basic activities such as running laps around the school or standing for extended periods of time. Like Yozora, she also finds crowds overwhelming, which further limits her stamina in group or public settings.

Kodaka Hasegawa
Rika develops a strong attraction to Kodaka after he saves her from a laboratory accident. She openly expresses her affection for him, often offering to “repay” him in ways that Kodaka firmly rejects. Unlike the other female members of the Neighbor’s Club, Rika makes her feelings clear and is both physically and romantically drawn to him. However, due to Kodaka’s oblivious nature or his deliberate avoidance, he does not directly acknowledge her advances.

Yozora Mikazuki
Rika generally treats Yozora with respect, addressing her as senpai and showing patience toward her limited knowledge of anime, manga, and games. Despite their differing interests, they frequently collaborate in teasing Maria Takayama and Sena Kashiwazaki, revealing a number of shared traits. Rika gradually attempts to bring Yozora closer to her worldview, including introducing her to BL-themed media. Although Yozora initially rejected Rika’s tastes as obscene, she later began to enjoy such content, allowing future viewings in the club. Their dynamic shifted over time, as Yozora ceased criticizing Rika’s eccentricities once Rika began responding with even more extreme comments, effectively turning the tables in their exchanges.

Sena Kashiwazaki
Rika and Sena share a complex relationship, often competing through teasing remarks. While Rika occasionally appears shocked by Sena’s own boldness, she also expresses envy toward Sena’s figure, echoing the insecurities of other female club members. Despite these tensions, Rika admits to admiring Sena for her straightforward yet surprisingly multifaceted personality. Both also share a passion for games, and Rika becomes defensive when others ridicule titles she enjoys, mirroring Sena’s reactions in similar circumstances.

Kobato Hasegawa
Rika and Kodaka’s younger sister, Kobato, have limited interaction throughout the series. Early on, Kobato is unsettled by Rika’s bluntness, particularly when Rika asks about the color of her undergarments. Over time, however, their relationship softens into a more neutral and occasionally friendly dynamic.

Rika’s given name, Rika (理科), is written with the kanji for “science” (理) and “subject” or “department” (科), directly reflecting her identity as a scientific prodigy. Her surname, Shiguma (志熊), combines “will” or “aspiration” (志) with “bear” (熊), though its meaning is less directly tied to her characterization.

The choice of kanji for her name underscores her defining trait within the series: her brilliance in science and invention, which contrasts with her eccentric and perverse personality.