Hajime Kiryū is a supporting character in When Supernatural Battles Became Commonplace. He is a tall young man with white hair and odd eyes, often seen wearing sunglasses and black clothing, a look that complements his dramatic personality. He is a graduate of the same high school that the main characters attend and was once a member of its literature club. More significantly, he is the older half-brother of Tomoyo Kanzaki, one of the main heroines.

In terms of personality, Hajime shares a profound passion for chuunibyou, the condition of acting out elaborate fantasy roles and delusions. He is immediately drawn to Jurai Ando, the protagonist, upon discovering Jurai's notebook of fantastical powers and terminology. However, while Jurai's fantasies often involve protecting others, Hajime's lean more toward grandiose and all-encompassing destruction. He is a man who has simulated the use of countless abilities in his imagination, which gives him a sharp tactical mind in actual combat. Despite this intense and dramatic exterior, Hajime is far from perfect. Having dropped out of college, he is a runaway from home who lives off a monthly allowance from his parents and relies on the hospitality of a former classmate, Hitomi Saito. His striking white hair is not natural but dyed, and his distinct odd-colored eyes are the result of colored contact lenses, which he sometimes forgets to remove, leading to eye infections.

Hajimes motivations are closely tied to the secret conflict known as the Fairy War, a battle between superpowered humans orchestrated by fairies for their entertainment, with the last eight winners granted a wish. Hajime is the leader of a group of ability users called Fallen Black. He is a highly skilled combatant, tasked by a fairy named Litia with crushing an organization known as F that opposes the war. His role in the story is primarily behind the scenes, acting as a major player in the larger supernatural world that the main literature club characters are only beginning to discover. He represents a path Jurai Ando might have taken, as the author has noted that Hajime embodies the original concept for the storys protagonist who gets fully drawn into supernatural battles.

Key relationships define much of his development. His bond with his half-sister, Tomoyo, is good despite him leaving home, and they keep in touch regularly. It is revealed that Tomoyo inherited her own chuunibyou tendencies from him, and the two once deeply shared in those fantasies. His friendship with Hitomi Saito is another cornerstone; she is his devoted second-in-command who supports him, and he seemingly lives at her home. His first meeting with Jurai Ando is a pivotal moment, as he becomes perhaps the one person who truly understands and validates Jurai's chuunibyou worldview, leading to an unusual camaraderie.

Hajime possesses a formidable supernatural ability that he calls Lucifers Strike. This power allows him to control gravity, enabling basic feats like walking on walls or ceilings by reversing gravitys direction. He can manipulate his own weight to be nearly zero for soft landings. In combat, Hajime shows masterful application of this ability. His signature and most devastating technique is Pinpoint Abyss, which creates a miniature black hole that can devour anything, including objects, light, and people, effectively serving as a one-hit kill. He has developed other gravity-based attacks, such as Mitsubachi, which concentrates gravity into a single point to create a piercing spear capable of penetrating most defenses, and Zakuro, which focuses gravity into a sharp line for a powerful slashing attack. His deep understanding of physics, born from years of delusional simulations, allows him to analyze and counter opponents abilities with genius-level intellect.

Throughout the narrative, Hajime undergoes significant development. Despite his role as a leader, he is considered pathetic and unpopular, with his members following him only due to his combat prowess. He is eventually revealed to have been the winner of a previous Fairy War, and he used his granted wish to initiate another war, effectively placing himself at its helm. He later gains the power of the fairies as an administrator, granting him reality-warping abilities, which he dislikes using as he considers it cheating. Ultimately, he is confronted by Jurai Ando about his true intentions for prolonging the war. His journey concludes with him returning to school and beginning a romantic relationship with Hitomi Saito.