I really like these! The main characters seem to be a mix of FR/LG main characters and R/S/E main characters. That's cool.
I really like Navy too. Reminds me a lot of Bakura from Yu-Gi-Oh! minus the shyness. I hope you do other art besides purely for the game. Or perhaps just draw more concept art for these characters and more :D
For future improvements (if you are looking for any, and if you're not here you go anyway) I'd say concentrate a little more on the head and face of your characters. Your main characters are definitely better than your rivals. They have better anatomical structure, posture and shading. I also find the necks in the front facing poses to be just a little too long for my liking, perhaps try and bring their heads down a little. Everything comes with time, but I like your character designs so far, so keep them coming d(^-^d)
Thanks! Well, I actually didn't based my characters in FR/LG, but in other concepts I made for my other stories, Crimson has a little resemblance to Red, but just in the hat and vest. And about Navy, just like my other concepts, I almost made his hair based a little on Bakura, but with some Blue/Gary hair style. Maybe I'm a little obsessed with saiyan hair styles, he he he!
Those first concepts I made for the mains and rivals were from 2010, so I have improved my drawing style at this moment, just wait until I publish more.
UPDATE: 3 more concept arts available in the gallery!