In the world of "How I Became a Superhero," having access to superpowers only comes to people who are born with them (until the advent of the drugs, of course). Through a series of flashbacks, the audience comes to learn that Moreau is one such person.
Moreau discovered his powers — to levitate objects — much later in life when he was working with Pack Royal. However, he struggled to properly harness them. His work with the superhero squad came to an end after he attempted to assist a hero named Gigaman (Clovis Cornillac). Although he was able to make his superpowers work, Moreau inadvertently caused a massive explosion that killed Gigaman in the process.
These revelations do a lot to explain aspects of "How I Became a Superhero" that are opaque at the start of the film. First, it gives the viewers a much better insight into why Moreau is such a sad sack. The worldbuilding makes it clear that — like many other superhero stories — having powers is as much of a burden as it is a blessing. Finding out about his own powers later in life was no doubt already difficult for Moreau and accidentally killing one of his allies with them definitely did not make that easier. Instead of continuing to hone his abilities, he suppressed his powers and kept them a secret from his colleagues.
Early in the film, we also meet Lily (Léonie Souchaud), a high school student with who Moreau clearly has a connection, although the nature of their relationship isn't explained. When she gets embroiled in the drug plot, we learn that she is the daughter of Gigaman and has inherited his abilities. This makes her a prime target for the film's main antagonist, who has been using superhumans themselves to manufacture his drugs.
