Yuuta Hibiki wakes up in the room of Rikka Takarada and notices two things: he has no memories, and he can hear a mysterious voice calling his name from a nearby room. On further inspection, he finds a robot—which introduces itself as Hyper Agent Gridman—behind the screen of an old computer. Much to Yuuta's surprise, Rikka cannot hear Gridman, nor can she see the ominous monsters looming over a thick fog as it envelopes the town outside. Another giant monster materializes in the city and proceeds to wreak havoc. Amidst the confusion, Yuuta is once again drawn to the old computer and merges with Gridman. Suddenly, he appears in the middle of the battle and is forced to fight the monster. Together with Rikka and fellow classmate Shou Utsumi, Yuuta forms the "Gridman Alliance" to defeat the monsters plaguing the city and find whoever is responsible for their emergence. [Written by MAL Rewrite]

"Weak Legs" Kenichi Shirahama would rather spend his time reading self improvement books than fighting. However, when he finally works up the courage to become strong and join his school's karate club, he is coerced into fighting a bullying upperclassman who is intent on getting him kicked out of the club. He is about to give it all up until he falls for his mysterious new classmate, Miu Furinji. In order to face this challenge, he undergoes rigorous training at the dojo she lives at, Ryouzanpaku. Some initial training by the masters there allow him to defeat his upperclassman, however his fighting prowess brings him to the attention of the powerful gang of delinquents, Ragnarok. Wishing to protect the things he loves and determined to have the strength to face the increasing adversity, he must learn various martial arts from the dojo's resident masters, taking Karate, Muay Thai, Ju Jitsu and Chinese Martial Arts and combining them to create his own fighting style!

Makoto Niwa meticulously tallies the amount of positive and negative youthful experiences he engages in as if to grade his own life. When his parents go overseas, he moves to a new town to live with his aunt, welcoming the change and ready for a fresh start. However, as ordinary as he had imagined his adolescence to be, he could never have taken the existence of an enigmatic long-lost cousin into account. Upon moving into his aunt's house, he discovers the cousin he never knew about: Erio Touwa. Despite being Makoto's age, she couldn't be more different: Erio chooses to wrap herself in a futon all day rather than to go to school. She even claims to be an alien, and with a speech pattern and personality to back it up, any chance of Makoto's dreamt-of normal life is instantly tossed out the window. As he meets a string of other eccentric girls in town, Makoto must face the possibility of seeing his youth points in the red. However, he might be surprised by how thrilling an abnormal youth can be. [Written by MAL Rewrite]

After seeing enough death and tragedy, the immortal Fushi secludes himself on an island, defending himself from enemy Nokkers. However, instead of attacking Fushi in isolation, Nokkers begin targeting the settlements outside of his reach in hopes of luring him out. Soon, a group known as the Guardians—led by Hisame, the descendant of the deceased warrior Hayase—finds Fushi. Inspired by how Fushi protected Janada Island from the Nokkers years ago, the Guardians have grown a considerable following and are recognized throughout the world. Initially reluctant, Fushi allows the Guardians to accompany him to the site of the Nokkers' recent attack. In their village, Fushi meets a few valuable allies, both new and old. But as the conflict with the Nokkers only leads to more loss, Fushi must find the inner strength to face his inevitable sorrow.