Dragon Quest Heroes: Rocket Slime is based in the fictional world of Slimenia, specifically in the capital city of Boingburg. It begins with four Slimes, Rocket, Hooly, Bo, and Swotsy, who are playing in front of the castle. Hooly has gotten his hands on a valuable flute, and in response to the flute being blown by Rocket, his father comes running over, forcing Hooly to stick the flute in Rocket's mouth. Afterward, an organization known as the Plob invades Boingburg, capturing 100 of its 101 inhabitants. Because he was distorted and long, the Plob mistakenly believed Rocket was not a Slime but a worm, and discarded him into Forewood Forest. There, Rocket begins his journey to rescue his fellow slimes, who have been locked up in large treasure chests.