"Rooster Fighter" centers on a rooster named Keiji, who possesses extraordinary strength and combat skills, enabling him to battle monstrous creatures threatening humanity. The narrative unfolds in a world where mysterious, destructive beasts emerge, wreaking havoc on cities and towns. Keiji, driven by a sense of duty and a mysterious past, takes on the role of a protector, using his unique abilities to confront these threats.

The story begins with Keiji encountering a young girl named Sayaka, who becomes a key figure in his journey. Sayaka, orphaned by the monsters, forms a bond with Keiji, and their relationship adds emotional depth to the series. As Keiji fights to protect humanity, he faces increasingly powerful adversaries, each with unique abilities and origins tied to the enigmatic emergence of the monsters.

Throughout the series, Keiji's past is gradually revealed, shedding light on his transformation into a formidable fighter and his connection to the ongoing crisis. The narrative explores themes of sacrifice, resilience, and the struggle between humanity and chaos. Supporting characters, including other fighters and survivors, contribute to the world-building and provide additional perspectives on the conflict.

The plot balances intense action sequences with moments of character development, creating a dynamic and engaging storyline. Keiji's battles are not only physical but also symbolic, representing the broader fight against despair and destruction. The series maintains a steady pace, blending episodic monster encounters with an overarching narrative that builds toward a climactic resolution.