Akachi is a member of the Twelve Shinsho, an elite group of warriors serving the imperial court in the mythical land of Amawakuni. He is a primary antagonist and a significant rival to his fellow Shinsho, Kannagi, with whom he shares a deep and painful history. In terms of appearance, Akachi is an adult male with black hair that falls to his neck and distinctive red eyes. He is often depicted wearing armor and bears a notable facial scar.

Akachi’s personality is defined by a chilling self-assurance and an unwavering drive for power. He operates from a philosophy where the only options are to submit or be submitted to, and he seeks to dominate others to prove his strength. While his actions are often ruthless, he is not portrayed as a purely evil villain. There is a depth to his character that suggests a more sympathetic figure, as his current antagonism is rooted in a tragic past and a sense of betrayal. This complexity is further highlighted by his past as a close comrade to Kannagi, making their present hostility all the more heart-wrenching.

Akachi’s primary motivation is tied to the throne of Amawakuni and his conflict with Kannagi. He seeks to defeat his former friend and make him submit, wanting him to suffer the pain of loss rather than simply taking his soul. His actions are also driven by events surrounding Kannagi’s half-sister, Emisu, whose story is central to the falling out between the two former friends. In his pursuit of power, Akachi is not above forming temporary alliances, as seen when he makes a chilling bargain with Masato Kadowaki, the rival of the protagonist, Arata Hinohara.

In the story, Akachi serves as a major obstacle for both Arata and Kannagi. He demonstrates his authority and cruelty when he forcibly takes Kannagi’s loyal Zokusho (a subordinate), Ohika, as his own. To ensure Ohika’s submission, Akachi threatens the lives of those under Ohika’s protection, including a pregnant woman named Fuyo, and then proceeds to kill others in the room despite his promises. He later engages Kannagi in a fierce battle, defeats him, and seizes his powerful Hayagami known as Homura, which contains Emisu’s spirit. Akachi’s actions force the main characters to raid his palace in an attempt to recover the stolen artifact.

Key relationships define Akachi’s role in the narrative. His bond with Kannagi is the most significant, evolving from close friendship to bitter enmity. The backstory reveals they once shared a comradery with a third individual, Emisu, and her fate is the source of a "sin" Kannagi supposedly carved into his own shoulder, which Akachi later references. Akachi also forms a strategic and unsettling alliance with Kadowaki, giving him one of his own eyes to empower him against Arata. This act demonstrates the lengths to which Akachi will go, but also his unpredictable nature, as Kadowaki finds he has gotten more than he bargained for. While Akachi is not the protagonist, his development is explored through flashbacks that provide crucial context for his motivations, showing the goodness and loyalty he once possessed before his fall from grace.

Regarding notable abilities, as a member of the Twelve Shinsho, Akachi is an exceptionally powerful warrior. He commands a Hayagami, a spiritual sword or entity that forms the core of a Shinsho’s power. He is skilled enough to easily defeat Kannagi in combat and take his Hayagami. Akachi also possesses unique and disturbing abilities, such as being able to physically remove his own eye and grant it to another person, as he does with Kadowaki, to enhance their power. He is also a master manipulator, capable of leading his enemies exactly where he wants them, as demonstrated when he anticipates and controls the movements of Arata’s group during their raid on his palace.