Junji is a hibakusha, an atomic bomb survivor from Hiroshima, whose life remains dominated by the catastrophe years later. He operates on society's fringes within the post-war black market, specializing in weapons trading. Profound hatred born from the bombing drives his actions, culminating in the killing of an American black marketeer. This act forces him to seek refuge with a yakuza boss, deepening his involvement in the criminal underworld for survival and retaliation.

He is the younger brother of Tomoko, a prostitute who suffered severe burns in the blast. The siblings frequent Stand Akauma, a bar gathering place for fellow survivors sharing their trauma. His relationship with Eiko, a pregnant young woman, represents a significant connection to potential hope or normalcy amid his struggles.

In the original manga narrative inspiring the anime, a character named Jin reflects a possible loose adaptation sharing core traits with Junji. Jin is depicted as a hitman who exclusively targets foreigners, particularly Americans, as revenge for the atomic bombing. He follows a path of violence and self-destruction, acknowledging the inevitability of his own demise. Despite his vengeful mission, he displays unexpected compassion. He encounters Peace, a blind girl, and her father, a destitute hibakusha suffering radiation sickness exacerbated by inadequate government support. Moved by their plight, Jin gives them money stolen from a victim. Mortally wounded after another assassination, Jin returns to them and offers his eyes for Peace's sight-restoring surgery before dying. This final act provides a chance for Peace's future.