Maika Tsuchimikado is the younger stepsister of Motoharu Tsuchimikado, a resident of Academy City, and a student at the prestigious Ryouran Maid School where she trains in domestic service. She was originally an orphan brought in to provide Motoharu with a cover identity for his spy activities within the city, though over time their bond grew into a genuine sibling relationship. Her integration into Academy City began with fabricated records, and her brother later enrolled her in the maid school, which she attends daily, proudly wearing her mandatory uniform at all times. She is approximately fourteen to fifteen years old, placing her around the same age as Index, and is noted to be one of the rare individuals in Academy City who has not undergone the esper development curriculum, possessing no supernatural abilities whatsoever.

In terms of appearance, Maika is a petite girl with short, blue-black hair that barely reaches her shoulders, often swept back by her bonnet. She has blue eyes and is almost always seen in her maid attire, which reflects her dedication to her chosen profession. A particularly distinctive and recurring visual trait is her tendency to be seen riding atop a cleaning robot, using long-handled tools to interact with and control these devices.

Maika possesses a personality that is energetic, straightforward, and marked by a unique speech pattern where she often stretches out the endings of her sentences. Despite the formal and polite nature typically associated with the vocation of a maid, she is gleefully unprofessional and casual with those she knows well, often dropping formal speech and honorifics altogether when she is comfortable with someone. She has a strong sense of duty and immense pride in her work as a maid-in-training, and she does not hesitate to reprimand others, particularly her brother Motoharu, when they voice stereotypical or subcultural ideas about maids that she feels trivialize or misrepresent the profession. Her relaxed manner and habit of speaking without using required polite suffixes would likely be problematic in an actual professional setting, but Maika herself remains largely unconcerned about such criticisms.

Maika is intensely devoted to her brother Motoharu, demonstrating what is often described as a very strong brother complex. She regularly visits his room to perform what she jokingly calls almost-girlfriend services, which include cooking for him, cleaning his room, massaging his health, and generally taking care of his domestic needs, a necessity given his complete lack of culinary skill. She has openly stated her preference for stories where the older brother falls in love with the younger sister, further reinforcing her apparent romantic affection for Motoharu. Her love for her brother is also expressed through her enjoyment of sibling-centric tales, and she once requested that Misaka Mikoto purchase an incest-themed manga for her.

Her primary motivation stems from a genuine desire to be helpful to others, which is the reason she chose to attend maid school. This desire was initially misinterpreted by her brother as a fear of abandonment, but he later came to recognize her innate kindness. In her daily life, she shares what she has with others and strives to be useful, finding fulfillment in supporting those around her. Her background as an orphan selected to create a family identity for a spy gives her actions a deeper context, as her chosen path reflects a true and earnest wish to contribute rather than a desperate attempt to prove her worth.

Throughout the story, Maika serves as a supporting character whose primary role is often tied to her domestic skills and her connection to her brother. She is well-acquainted with Kamijou Touma and Index, frequently encountering them at Motoharu's dormitory, and she has friendly, warm interactions with them. She also provides Index with directions to Touma's school on one occasion and even helps Touma search for Index when she goes missing. Her skills as a cook are exceptional; Touma himself remarks that she could charge money for her meals, and she can easily discern the ingredients and cooking processes of high-class cuisine just by evaluating a dish for a short period. She is self-demanding when it comes to cooking and can get fired up if she sees someone create high-class cuisine, developing a friendly but competitive culinary rivalry with Itsuwa, another skilled cook in the series.

As part of her elite training at Ryouran Maid School, Maika takes on practical assignments at various locations, including Tokiwadai Middle School, where she interacts with Misaka Mikoto. Her other activities include selling authentic maid bento boxes during the Daihasei Festival and helping to prepare food for the Tokiwadai dormitorys opening events. In later story developments, Maika becomes a target due to her relationship with Motoharu, serving as a potential hostage or bargaining chip against him because of his involvement with various organizations. During the Agitate Halation Project, Motoharu fakes her death to deter enemies, tricking her into cleaning a factory as extracurricular work before staging a fire at his dormitory. She later vents frustration at receiving no school credit for the labor. In the events surrounding Aleister Crowley, she flees Academy City with Motoharu after he attacks Aleister for endangering her. During their escape, a cursed magic sword pierces her chest, summoning chain-like creatures, though she remains oblivious to the curse and her own peril while her brother and allies work to save her. Her unwavering loyalty to Motoharu is central to her character, and she anchors him morally, countering his darker choices with persistent compassion and dedication.