Plot

Following Kick-Ass' heroics, other citizens are inspired to become masked crusaders, but Red Mist leads his own group of evil super-villains to get revenge, kill Kick-Ass, and destroy everything he stands for.

After Kick-Ass' insane bravery inspires a new wave of self-made masked crusaders, led by the badass Colonel Stars and Stripes, our hero joins them on patrol. When these amateur superheroes are hunted down by Red Mist -- reborn as The Mother F%&*^r -- only the blade-wielding Hit Girl can prevent their annihilation. When we last saw junior assassin Hit Girl and young vigilante Kick-Ass, they were trying to live as normal teenagers Mindy and Dave. With graduation looming and uncertain what to do, Dave decides to start the world's first superhero team with Mindy. Unfortunately, when Mindy is busted for sneaking out as Hit Girl, she's forced to retire, leaving her to navigate the terrifying world of high-school mean girls on her own. With no one left to turn to, Dave joins forces with Justice Forever, run by a born-again ex-mobster named Colonel Stars and Stripes. Just as they start to make a real difference on the streets, the world's first super villain, The Mother F%&*^r, assembles his own evil league and puts a plan in motion to make Kick-Ass and Hit Girl pay for what they did to his dad. There's only one problem with his scheme: If you mess with one member of Justice Forever, you mess with them all.—Universal Pictures

Four years after the death of Damon Macready / Big Daddy and defeating Frank D'Amico, Dave Lizewski, is bored after having retired from fighting crime as Kick-Ass.

Dave Lizewski (Aaron Taylor-Johnson) begins training with Mindy Macready / Hit-Girl (Chloe Grace Mortez) to become a proper hero. Mindy is having problems of her own after the death of Big Daddy & is taking isolation very hard, so she agrees to team up with Dave. Dave and Mindy both studied in high school. Marty and Todd are Dave's best friends. Dave hides his partnership with Mindy from his friends and his girlfriend Katie.

Meanwhile, Chris D'Amico (Christopher Mintz-Plasse) and his mother argue over the death of his father. Chris says that Kick-Ass killed his father with a bazooka, but his mother insists that he died in a fire. Frustrated, Chris kicks the tanning bed his mother is using, causing it collapse on Chris' mother, killing her. Now with control over his family's money, Chris reinvents himself as super-villain, The Motherf****r.

The Motherf****r adapts a BDSM suit for his costume, and assembles a gang of super-villains called the Toxic Mega C**TS with his bodyguard Javier (John Leguizamo), swearing vengeance on Kick-Ass. The other leading members of the Toxic Mega C**TS include African-American UFC fighter Black Death (Daniel Kaluuya), short-stature mob enforcer The Tumor (Andy Nyman), ex-Triad gang member Genghis Carnage (Tom Wu), and the only woman on the team, former Russian bodyguard Mother Russia / Katarina Dombrovski.

Dave goes on his first mission and lures some punks to attack him and gets beaten up instead. Mindy intervenes to save Dave but attracts the attention of the police. Marcus hears the news on the radio and rushes home, as Mindy had claimed to have fever and was supposed to be in bed. Mindy's guardian, Marcus (Morris Chestnut), discovers she is still fighting crime (as he finds her in bed, but she had blood on her temples) and makes her promise to give it up. Dave's girlfriend, Katie Deauxma (Lyndsy Fonseca), has noticed Dave behaving strangely and breaks up with him, believing he is cheating on her with Mindy.

Kick-Ass joins the superhero team Justice Forever, led by Colonel Stars and Stripes (Jim Carrey). It includes Battle Guy (Clark Duke) (Dave's friend, Marty), Dr. Gravity (Donald Faison), Insect Man (Robert Emms), Night-Bitch (Lindy Booth) seeking to avenge the murder of her sister, and the parents of a missing child named Tommy (Steven Mackintosh & Monica Dolan). The team starts out working at soup kitchens and patrolling the streets before taking on the larger task of shutting down a brothel. Kick-Ass begins a relationship with Night Bitch, and he and Marty try to get their friend Todd (Augustus Prew) involved with heroics. Dave and Marty (who is also a member of Justice Forever as Battle Guy), alienate their friend Todd from participating in their heroics by calling his superhero persona "Ass-Kicker" an obvious knockoff of Kick-Ass.

Mindy tries leading a normal life. Brooke (Claudia Lee), one of the popular girls, suggests Mindy try out for the dance team at school, but when Mindy wows the audience with her audition, Brooke is unhappy. Dave tries to convince Hit-Girl to join Justice Forever, but she refuses and promptly asks a boy to take her on a date. The date ends up as a cruel prank, leaving Mindy abandoned in the forest to walk home alone. Dave consoles the tearful Mindy and encourages her to beat the mean girls at their own game. The next day, Mindy does so with verbal put-downs and a crowd-control shock baton, resulting in her suspension from school. Meanwhile, Mr. Lizewski (Garrett M. Brown) discovers Dave is Kick-Ass after finding his superhero costume in his room and they have an argument which leads Dave to leave home.

The Motherf****r assembles a gang of super-villains and establishes an underground lair. He finds Colonel Stars and Stripes and has Mother Russia (Olga Kurkulina), a massive Russian ex-con and former KGB agent, decapitate him before taunting Justice Forever on Twitter. He then tracks down Night-Bitch and attempts to sexually assault her but fails due to impotence and has her beaten up instead. When police arrive, Mother Russia kills all 10 officers, resulting in a police clampdown on both costumed villains and vigilantes. When the police track Dave through his IP address, Dave's protective father claims he, not Dave, is Kick-Ass.

The Motherf****r, unconvinced the real Kick-Ass has been caught, learns from Todd, who had inadvertently joined the Motherf****r's group, that the man identified as being Kick-Ass is actually his father. The Motherf****r has Mr. Lizewski killed in jail and sends a photograph to Dave, revealing his true identity as Chris D'Amico. Grief-stricken, Dave vows to never put on the Kick-Ass costume again, as he had promised his father. At the funeral, the Motherf****r's gang ambushes and kidnap Dave.

Afterwards, Dave, Mindy and the remaining members of Justice Forever, joined by a resurgence of masked Do-Gooders, battle and defeat the outnumbered Toxic Mega C**TS. Mindy pursues their fleeing van, killing all but one of its occupants, rescuing Dave, and convincing him to confront the Motherf****r. Dave and his superhero friends attack the villain's lair where they are preparing to have Kick-Ass fed to a shark. While Kick-Ass fights the Motherf****r, Hit-Girl struggles against Mother Russia. Hit-Girl tricks Mother Russia into injecting her with a syringe of adrenaline. This gives her the strength to kill Mother Russia with shards of glass. Fighting on a rooftop, the Motherf****r falls through a skylight, but Kick-Ass grabs him. The Motherf****r refuses help and falls, landing in his own shark tank where he is mauled. Later on, Justice Forever decide to give up their superhero duties for good.

Justice Forever decides to take a break from its superhero duties, helping people in their ordinary lives instead. Mindy tells Dave that she is leaving New York due to being wanted for murder, but that the citizens need Kick-Ass, then kisses him goodbye. As police officers raid Marcus's home to investigate Mindy's whereabouts, Dave accepts the responsibility and begins training and upgrading his equipment, with a much more muscular physique.

In a post-credits scene, Chris, who has survived the shark attack, and whose limbs and genitals were bitten off by the shark, complains for attention over an out of reach cup of water.