Jurai Andou is a seventeen-year-old student attending the私立泉光高校 (Shiritsu Izumikou High School), where he is a member of Class 2-1 and the literature club. He has an O blood type, though he prefers to refer to it as "King type" as part of his elaborate self-image. Andou is best described as an entrenched "chunibyo," a person who suffers from "Middle School Second-Year Syndrome," meaning he is deeply invested in grandiose fantasies, dark mythical motifs, and a fictional persona he has constructed for himself. He calls himself "Guiltia Sin Jurai" and has named the supernatural abilities of all his friends, carrying a notebook he refers to as the "Red Bible" (Blood Vivre) which is filled with his ideas and lore. Despite his eccentric and often loud behavior, he is genuinely kind-hearted, compassionate, and surprisingly pragmatic, often serving as the moral center of his friend group.

His core motivation is a deep-seated love for the "cool" and dramatic aspects of supernatural battles and heroism. Unlike many who might be disappointed by a weak power, Andou is simply thrilled to have any ability at all, as it validates his long-held fantasies. At the same time, he is driven by a strong sense of responsibility. He is the most level-headed member of the literature club when it comes to the practical use of their powers, consistently warning the others to keep their abilities secret and to never use them to harm others. He becomes a central figure in the story not because of his power, but because of his role as the group's emotional anchor and strategist. He helps each of his friends confront personal issues and devises plans when conflict arises, often using his wits rather than brute force. His relationship with his childhood friend, Hatoko Kushikawa, is particularly significant, as her eventual frustration with his chuunibyou rants forces him to confront the gap between his fantasies and her needs.

Andou's notable abilities are as ironic as his personality. His supernatural power is called "Dark and Dark," which manifests as a black flame that is completely safe and cannot burn anything, only producing a low-temperature heat. He embraces this uselessness, believing a power's purpose is to look impressive rather than cause destruction. However, his power has a dangerous second form, "Dark and Dark of the End" (or "the one who draws the final curtain"). When fully awakened, his flames become incredibly destructive and burn with an intensity that cannot be extinguished. This power comes at a terrible cost, as the flames consume his own body as well, forcing him to rely on his friends to sever the burning limb to save his life. He is also more academically intelligent than his behavior suggests, earning high grades and possessing a broad knowledge of mythology and trivia, which he incorporates into his chuunibyo persona.

Throughout the story, Andou shows a conflicted journey regarding his identity. While he outwardly embraces his chunibyo nature, an incident in middle school, where his friends betrayed him and mocked his hobbies, led him to try and abandon his fantasies entirely. He was only inspired to return to this lifestyle after an encounter with a mysterious silver-haired girl (who was actually his classmate Tomoyo Kanzaki in disguise). As the series progresses, particularly in the light novels, Andou grapples with the desire to grow up. He considers giving up his chuunibyo tendencies for the sake of Hatoko's feelings and to accept reality. He even temporarily succeeds in "graduating" from his delusions with the help of a friend,桐生一 (Hajime Kiryu). However, this change is not permanent, and even as an adult, Andou ultimately retains the core of his chuunibyo spirit, suggesting that it is an inseparable part of his personality rather than just a phase.