As a child, Riki Naoe's narcolepsy diagnosis caused him to retreat from the world after the tragic deaths of his parents. But his life takes a turn when he is invited by Kyousuke to join the Little Busters, a group of misfits who fought evil and enjoyed life together with Masato, Kengo, and Rin. Even after their high school graduation, the tight-knit group remains together. But with Kyousuke's impending departure, the Little Busters decide to form a baseball team. The problem is, they need more members. Riki must step up and recruit new teammates. Their journey to uncover the "secret of this world" begins when Rin discovers a mysterious letter attached to her cat. To solve the mystery and uncover the hidden truth, the Little Busters must complete a series of specific tasks.