These two are brother/sister (respectively) but Cagix is an actual being whilst Vexx is more of a... spirit, if you must. He was derived from what was left of Phoenix's and Cage's soul. He's more or less the dark matter while Cagix is the good matter. They both control Arinthian but due to one controlling night and the other day, they are forbidden from ever meeting and are forced to chase eachother around the planet for eternity. Vexx longs to have a body and eventually he possesses one.