Mirai Andō is a lightning demon who appears in human form as a fourteen-year-old girl with long orange hair and blue eyes. She is notably small in stature, standing only 147 centimeters tall, and despite her age she attends Miyasaka High School as a student. Her true nature as a lightning demon is the foundation of her character, and she possesses the ability to generate and control lightning as her primary supernatural power. This ability, however, comes with a critical limitation: she can only release her lightning powers after being kissed on any part of her body by Kurenai Gekkō, the student council president with whom she is bound by a contract.

Mirai was originally sent by Kurenai Hinata, Gekkō's younger twin brother, to assassinate Gekkō. Her mission failed when Gekkō overpowered her and instead forced her into a contractual bond. This shift from enemy to subordinate defines her early role in the story. Although the contract was initially imposed against her will, Mirai later develops genuine romantic feelings for Gekkō and becomes deeply attached to him. Her loyalty to him grows over time, and she serves as a member of the student council at Miyasaka High, which functions as the central group through which many of the story's conflicts unfold.

Mirai's personality is energetic, loud, and noisy. She is often enthusiastic and expressive, rarely holding back her emotions or opinions. She has a fondness for Dr. Cinnamon soda, a branded carbonated drink that she frequently consumes. Despite her energetic exterior, she is capable of seriousness and determination when the situation demands it, particularly in battle or when Gekkō is threatened. Her motivations are closely tied to her contract with Gekkō and her feelings for him. She seeks to protect him and support his goals, and she desires to remain close to him both as his contracted demon and as someone who cares for him personally.

Within the story, Mirai occupies the role of a contracted familiar and a combat ally. She is one of the key members of the student council alongside Gekkō, Kurogane Taito, Saitohimea, and others. Her lightning powers make her a formidable opponent in battles against the various demonic and magical threats that arise, and her unique activation requirement adds a layer of dependence on Gekkō that shapes their dynamic. She is also a source of comic relief due to her loud and impulsive nature, balancing the more serious tones of the narrative.

The most significant relationship in Mirai's life is with Kurenai Gekkō. What begins as a forced master-servant arrangement evolves into a mutual attachment, with Mirai falling in love with him and Gekkō coming to rely on her presence and abilities. She also interacts with Kurogane Taito and Saitohimea, the other central characters, often as an ally and occasional rival in the student council setting. Her relationship with Hinata, who initially deployed her as an assassin, is adversarial and rooted in the circumstances of her original mission.

Mirai's development is marked by her transition from a tool sent to kill to an individual who makes her own choices about loyalty and love. She grows more comfortable in her role within the student council and becomes more protective of those she considers her allies. Her powers remain consistent, but her understanding of her own agency and her feelings for Gekkō deepen as the story progresses. She remains a lightning demon first and foremost, but her identity becomes increasingly tied to the bonds she forms rather than solely to her original mission.