Good point, Lexi is a Nobody. His friend, Iz and him invented a strategy to get into the Organization. Lexi's Somebody, Eli decided to be the one that got turned into a Heartless. And, Saix knowingly brought Lexi into the Organization as Number XVI, the Sparks of Flames. However, Lexi betrayed Iz and decided to work against him.
The kid that ran into Axel is named Gway. Gway actually has Sora's heart within him.