Marty originally told the members of the Justice Forever team that he witnessed his parents murdered and eaten and that the murderer had used his parents credit cards for pay-per-view porn. Later when Kick-Ass joins the team, Dave recognizes Marty's voice and informs the team that Marty's parents are still alive.
Major Story Arcs
Battle Guy is seen among the faces of the other people who are stepping up as masked heroes.
Kick Ass 2
When Kick Ass first meets the Justice Forever team, Battle Guy tells his back story, about his parent's murder, but David recognizes Marty's voice and calls him out on the fact that his parents are still alive. Battle Guy takes off his mask and apologizes to the group for lying, claiming he felt like he need a dark past to be excepted. Colonel Stars, understands and pats Marty on the back letting him know it's okay.
Battle Guy and Kick Ass are seen together a lot more, both because they go to the same school and are about the same age. They are together when the team hits Mister Kim's whore house. Then they bring their friend Todd into the team. Marty goes with David to see Katie in the hospital.
Then when David's dad, Mr. Lizewski, is taken to Ryker's Island, David stays with Marty. Marty is there when David finds out his dad is dead and Marty is there at the funeral for Mr. Lizewski and when the Red Mist's crew shots up the funeral.
Later when Red Mist's team of super villains battle Kick Ass team of superheroes, Battle Guy and Todd try to find someplace to hide and witness Hit Girl kill Mother Russia. Battle Guy makes it out of the fight alive and meets back up with Kick Ass later with Todd and the three seem to avoid being arrested.