"Shine On! Bakumatsu Bad Boys" is set during the Bakumatsu period in Japan, a time of political upheaval and transition as the Tokugawa shogunate nears its end. The story revolves around a group of young men who are part of the Shinsengumi, a special police force tasked with maintaining order in Kyoto. The series focuses on their struggles, camaraderie, and the challenges they face as they navigate the turbulent era.

The protagonist, Toshizou Hijikata, serves as the vice-commander of the Shinsengumi and is known for his strict demeanor and unwavering loyalty to the group's cause. Alongside him is Isami Kondo, the charismatic leader who inspires the group with his vision of a unified Japan. Other key members include Souji Okita, a skilled swordsman with a playful yet deadly nature, and Hajime Saito, a stoic and disciplined fighter. The group also includes younger members like Heisuke Toudou and Shinpachi Nagakura, who bring youthful energy and idealism to the team.

The narrative explores the internal and external conflicts faced by the Shinsengumi as they confront rival factions, political intrigue, and the shifting loyalties of those around them. The series delves into the personal lives and motivations of the characters, highlighting their bonds and the sacrifices they make for their ideals. Themes of honor, duty, and the cost of revolution are central to the story, as the characters grapple with the moral complexities of their actions in a time of war and uncertainty.

As the Bakumatsu period progresses, the Shinsengumi find themselves increasingly at odds with forces seeking to overthrow the shogunate, including the imperial loyalists and other revolutionary groups. The series portrays key historical events and battles, blending historical accuracy with dramatic storytelling to create a compelling depiction of this pivotal era in Japanese history. Through its focus on the Shinsengumi, "Shine On! Bakumatsu Bad Boys" offers a nuanced exploration of loyalty, identity, and the human cost of political change.