The seemingly unimpressive Saitama has a rather unique hobby: being a hero. In order to pursue his childhood dream, Saitama relentlessly trained for three years, losing all of his hair in the process. Now, Saitama is so powerful, he can defeat any enemy with just one punch. However, having no one capable of matching his strength has led Saitama to an unexpected problem—he is no longer able to enjoy the thrill of battling and has become quite bored. One day, Saitama catches the attention of 19-year-old cyborg Genos, who witnesses his power and wishes to become Saitama's disciple. Genos proposes that the two join the Hero Association in order to become certified heroes that will be recognized for their positive contributions to society. Saitama, who is shocked that no one knows who he is, quickly agrees. Meeting new allies and taking on new foes, Saitama embarks on a new journey as a member of the Hero Association to experience the excitement of battle he once felt.

ACCA—a national body of the kingdom of Dowa that provides public services to the citizens of the country—was established as part of the peace settlement between the king of Dowa and the 13 states of the country during a revolt. One hundred years later, Dowa is in a period of unprecedented peace, due in part to the ACCA system. However, rumors of a coup d'état start to surface. Jean Otus, the second-in-command of the inspection department of ACCA, is charged with inspecting all 13 state branches. What will he discover as he performs his audit? Intriguing and mysterious, ACCA: 13-ku Kansatsu-ka is a politically-themed mystery that reveals a world of diverse cultures and lifestyles, with intricate connections between its characters, as the truth of the coup d'état slowly unfolds.

When ordinary high school student Aoba Watase is suddenly targeted by a giant robot known as a "Valiancer," he is saved by his mysterious classmate Hina Yumihara. After revealing that she and their robotic enemy are from the future, Hina suddenly propels Aoba 70 years forward in order to prevent his death. Upon arrival, Aoba finds himself in the cockpit of a Valiancer called "Luxon," stuck in the midst of a firefight between the military forces of the Free Pact Alliance (FPA) and Zogilia Republic. After he shows high compatibility with an FPA pilot named Dio Weinberg, the two perform a successful "coupling," allowing them to share experiences and subsequently increase their capabilities and skills. Although Aoba is able to survive this unexpected battle, he is taken into custody by the FPA ship Cygnus, who wishes to interrogate him. While the student's main concern is whether he will ever be able to return home, what he doesn't realize is that he is about to get caught up in a war to protect the world.

The two part finale of Buddy Complex television series deals with the final battle between the Free Treaty Alliance and the space division of Zogiria, lead by an elderly Bizon, as Earth and time itself hang in the balance.