When office worker Nam-woo receives a package from childhood friend Jun-ho it transports him back to their last summer together. Back to their hometown in a small fishing village it the last few days before Jun-ho left for boarding school in Seoul. When a marble and an abandoned lighthouse had the power to transport him to a fantastic world where a mysterious flying girl named Mari lived.

A tranquil forest and all of its residents must face the destruction of man. A squirrel, born and raised in the forrest, fights to defend his home and faces trials and adversities along the way.

Astro Boy appears to be a normal, playful kid, yet he is a robot capable of both flying and incredible strength. Living with his parents in a small town where humans and robots coexist, he has many friends thanks to his cheerful nature. Eager to learn and try new things, Astro and his companions often embark on exciting adventures. But their explorations are met with unexpected troubles when the wicked criminal Hamegg—joined by his accomplices Gora, a pink gorilla robot, and Professor Flau—interferes with their endeavors. As the little robot boy and his group bravely face challenges, their efforts become part of a journey to discover the world's values and wonders.

Fourth season of the Ketsuekigata-kun! series.