Question: how laxus become a dragon slayer?
Answer: At some point during his childhood, Laxus' father, Ivan Dreyar, implanted Dragon Lacrima into Laxus' body, granting him Lightning Dragon Slayer Magic. As he grew up, Laxus constantly felt trapped in a shadow by being the grandson of Makarov, and, as a result, felt he never got the credit he deserved.