Simon and Kamina were born and raised in a deep, underground village, hidden from the fabled surface. Kamina is a free-spirited loose cannon bent on making a name for himself, while Simon is a timid young boy with no real aspirations. One day while excavating the earth, Simon stumbles upon a mysterious object that turns out to be the ignition key to an ancient artifact of war, which the duo dubs Lagann. Using their new weapon, Simon and Kamina fend off a surprise attack from the surface with the help of Yoko Littner, a hot-blooded redhead wielding a massive gun who wanders the world above. In the aftermath of the battle, the sky is now in plain view, prompting Simon and Kamina to set off on a journey alongside Yoko to explore the wastelands of the surface. Soon, they join the fight against the "Beastmen," humanoid creatures that terrorize the remnants of humanity in powerful robots called "Gunmen." Although they face some challenges and setbacks, the trio bravely fights these new enemies alongside other survivors to reclaim the surface, while slowly unraveling a galaxy-sized mystery. [Written by MAL Rewrite]

During recess, Olivia, a foreign transfer student who doesn't know English, plays a game of "look-the-other-way" with Hanako Honda, a loud-mouthed airhead. Their rowdy behavior spurs the ire of Kasumi Nomura, a deadpan loner constantly teased by her older sister for her tendency to lose games. Not willing to compete, Kasumi declines Olivia's offer to join the fun, but eventually gets involved anyway and dispenses her own brand of mischief. Soon, a strange friendship blossoms between the peculiar trio, and they decide to form the "Pastime Club," where they are free to resume their daily hijinks. Whether it be failing to learn English, trying desperately to become popular, or getting caught by teachers at the wrong time, school life will never be boring when the girls of Asobi Asobase are up to their hilarious antics.

Chiyo Mihama begins her high school career as one of the strangest students in her freshman class—a tiny, 10-year-old academic prodigy with a fondness for plush dolls and homemade cooking. But her homeroom teacher, Yukari Tanizaki, is the kind of person who would hijack a student's bike to avoid being late, so "strange" is a relative word. There certainly isn't a shortage of peculiar girls in Yukari-sensei's homeroom class. Accompanying Chiyo are students like Tomo Takino, an energetic tomboy with more enthusiasm than brains; Koyomi Mizuhara, Tomo's best friend whose temper has a fuse shorter than Chiyo; and Sakaki, a tall, athletic beauty whose intimidating looks hide a gentle personality and a painful obsession with cats. In addition, transfer student Ayumu Kasuga, a girl with her head stuck in the clouds, fits right in with the rest of the girls—and she has a few interesting theories about Chiyo's pigtails! Together, this lovable group of girls experience the ups and downs of school life, their many adventures filled with constant laughter, surreal absurdity, and occasionally even touching commentary on the bittersweet, temporal nature of high school. [Written by MAL Rewrite]