As a child, Riki Naoe isolated himself from the world due to a narcolepsy diagnosis following the tragic deaths of his parents. However, Riki is rescued when, on one fateful day, a boy named Kyousuke recruits him into a group calling themselves the Little Busters. Alongside Masato, Kengo, and Rin, these misfits spend their childhood battling evil and enjoying their youth. Years pass, and even in high school, the close-knit teammates stay together. Kyousuke decides to revive the Little Busters by forming a baseball team, as it will be his final school year with them. They face a problem, though: there aren't enough members! The situation has reversed, for it is now Riki's turn to reach out and recruit new friends into the Little Busters, just as Kyousuke once did for him. Then, an omen appears—Rin finds a strange letter attached to her cat, assigning them the duty of uncovering the "secret of this world" by completing specific tasks. Just what is this secret, and why is it being hidden? It's up to the Little Busters to find out!