Well, the next episode answers that, although, it's a bit unbelievable.
Would you believe Reiji is a prince from another world? Well, that's what he said, right?
Anyway, episode 3 promises Zeon loyalty, a budding romance (I'd like to think) and Sei's complete gunpla Build Strike as our two protagonists compete on round 1 of the Gunpla Battle Championship!
*I'm such a trying-hard-reviewer-wanna-be.
Here's a youtube video of the episode! Enjoy ^_^
Gundam Build Fighters Episode 2: The Crimson Comet
Gundam Build Fighters Episode 1: Sei and Reiji