After an embarrassing high school class reunion with their successful classmates, who have proper jobs, relationships, and even children, the Matsuno sextuplets return home to sulk about their status as NEETs. They spend the night drinking away their sorrows, eventually falling unconscious, until they awaken in a strange world of memories, centered around one of the brothers' biggest high school regret. As the sextuplets navigate this memory world, they encounter their embarrassing past selves from high school, as well as those of their friends. All the while, they try to uncover whose regret was great enough to trap them in this strange world, so that they can make their way back to reality. However, they're running out of time; this world of memories is unstable, and the sextuplets may lose their chance to make things right if they're too slow....

Bundled with the 13th limited-edition volume of the manga.

After his first appearance on the competitive world stage, Haruka is held captive by the swimming of the unmistakable champion, Albert, and feels like he's lost his way. With the current state of things, his swimming and what the water means to him are called into question. Haruka begins to sink to the bottom of the murky water as he struggles on his own. Pushed on by a restless urge in his heart, Haruka purposefully puts himself through a rigorous and intensive training regiment, relentlessly devoting himself to practice. In his heart, Haruka knows that he's pushing himself beyond his limits both physically and mentally. His friends can do nothing but watch over and have faith in him. Memories of Albert's cold, dry swimming keep replaying in his mind. I have to get faster, I have to become stronger. I have to compete against Albert again. Haruka unleashes his stroke to cut through the heavy, indifferent water. His friends draw closer to watch. What scenery will Haruka see at the end of this struggle＊──! (Source: Free! website, Translated)

Jeff Bogard was a master of the Hakkyokuseiken martial arts school and the guardian of its secret techniques. Coveting this knowledge, Geese Howard, the most powerful man in South Town, challenged and murdered him in front of his adoptive sons Terry and Andy Bogard. Under the guidance of their mentor Tung Fe Rue, the brothers dedicate their lives to training in the ultimate art to avenge their father. 10 years later, Geese promotes a martial arts tournament known as the King of Fighters. Terry and Andy join their friend Muay Thai champion Joe Higashi and enter the competition in order to finally face Geese in combat.