Following the events of Waluigi Unleashed III, Waluigi is hiding in the desert, having successfully avoid 64 assasination attempts by Lanky Kong's death squads. Hearing rumors that a resistance by loyalists of the former Primate Alliance junta still exists deep in the jungles of the Banana kingdom, the man goes forth, eager to bring ruin to his worst enemy.
Waluigi arrives in-extremis to save the resistance and its leader Colonel Bluster Kong from annihilation by the Party Monkey spec ops, but both parties are surprised by the arrival of an unexpected interloper: Mr. Eraser.
Mr. Easer presents himself as the sole survivor of the Fifth Dimension, which was entirely destroyed by Lanky Kong in an event know as the Genoblast. He then goes to explain that from a single dimensional genocider, Lanky Kong is a "dimensional cancer", an entity whose various multiversal permutations have caused untold deaths and carnage. Waluigi volunteers to destroy all incarnations of Lanky Kong and maintain the stability of the multiverse.
Traveling through dimensions and fighting foes such as Pink Gold Lanky Kong, the dissapointing robotic dupplicate Janky Kong and the martial arts expert Lanky Long, Waluigi absords enough of the slain Lanky Kong souls to unlock their power and storm Lanky Kong's fortress, Blue Banana.
Finally reaching the top and subduing Lanky Kong in a shitty and frustrating series of quick-time events, Waluigi prepares to execute the orang-utan until Lanky reveals the truth: Mr. Eraser wasn't entirely correct in claming to be the sole survivor of the Fifth Dimension: Lanky Kong was native to the dimension and settled in the current one after. Thus, he is not this dimension's native Lanky Kong; rather, Waluigi, pointing out to their ability to stretch themselves for the pleasure of the audience, lack of style, abscence of grace, and funny face. Despair soon takes over Waluigi.
As the screen fades to black, the sound of a gunshot is heard,