Aki Hayakawa

A male member of the Public Safety Devil Hunters' Special Division 4, and Denji's senior by three years. He ties his hair at a high position on the back of his head. His parents (voiced by Yōji Ueda and Eri Saitō) and younger brother Taiyo (voiced by Mana Nakatomi) were killed by the Gun Devil, leading him to become a Devil Hunter for revenge. He is dedicated to defeating the Gun Devil, possessing a strong conviction and high skill level, to the point of being unafraid of death. Although he usually acts coldly, he is inherently kind-hearted and compassionate. He has a long-standing partnership with Himeno, and they share a deep mutual trust. Additionally, he holds Makima in high regard as a "savior."

At the beginning of the story, he is contracted with the Fox Devil and the Curse Devil, using their powers in battle, but his lifespan is significantly reduced due to repeated use of devil powers. After being abandoned by the Fox Devil and unable to use the Curse Devil's power due to a shortened lifespan, he forms a new contract with the Future Devil and partners with the Angel Devil, fighting with a sword made from the Angel Devil's lifespan weapon.

After Denji and Power join the Public Safety Devil Hunters' Special Division 4, he lives with them as their supervisor and guardian. Initially, he struggles with Denji and Power's selfishness, but as they live together, they become irreplaceable to him. During the Gun Devil extermination mission, which was supposed to be his long-cherished wish, he becomes so afraid of losing them that he requests not to participate. However, he is controlled by Makima's abilities to intercept the Gun Devil, and his body is taken over by the Gun Devil, turning him into a Gun Fiend who attacks Denji. In his confused state, he envisions playing a snowball fight with Denji while starting a massacre, but ultimately, he is defeated by Denji, who responds to the cries for help from the people. In his final moments, his spirit is filled with happiness as he reunites with his brother and finally plays catch with him, something he couldn't do before.