After the events of the first film, the unconventional superhero Dave Lizewski, known as Kick-Ass, decides to retire his crime-fighting alter-ego and return to a normal life. Meanwhile, Mindy Macready aka Hit-Girl promises her guardian, Detective Marcus Williams, that she will give up her vigilantism and try to live a normal teenage life. However, Dave soon grows bored of regular life and desires to start patrolling the streets again. He reaches out to Mindy to team up, but she is reluctant due to her promise. Eventually, Dave finds a new group of self-styled superheroes led by Colonel Stars and Stripes and joins them. Inspired by Kick-Ass, these citizens have donned costumes to become real-life heroes.

Feeling left out and searching for a sense of purpose, Mindy tries to fit in at high school but becomes disillusioned by the pettiness of the other students. Concurrently, Chris D'Amico, seeking revenge for his father's death, reinvents himself as the super-villain The Motherf**ker and assembles a team of his own. His objective is to destroy Kick-Ass and anyone associated with him. This escalating conflict between heroes and villains draws various characters into the fray, presenting challenges that test their resolve and identities as both normal people and extraordinary figures in a world that is increasingly blurring the lines between the two.