I'm not going to reveal the entire story, but many should have already bought the game by now anyway.
As for my original question, Summoner, I suppose that's a good point, considering you brought up the alignment system from
Dungeons and Dragons, but personally, when it comes to soldiers in battle, there are two types: warrior and guardian. A warrior is someone who fights offensively, to attack the enemy. On the other hand, a guardian is someone who fights to protect.
Minor spoilerVentus seems to strike me more as a guardian, as well as a pacifist (as quoted by Vanitas): one who tries to avoid unnecessary fighting.
Also, I should note that while Ventus and Aqua are much like Sora and Kairi, it would seem to me as if they had their genders switched around; Aqua strikes me as a female Sora (quite brash), and Ventus strikes me as a male Kairi (not very brash).
Again, minor spoilerBoth Ventus (after his rejected darkness was extracted from him) and Kairi have hearts that are made from the purest of light, and ended up losing their hearts at one point. The difference between the two is that Ventus has more "fight" in him than Kairi has in her (although she did wield a Keyblade, and that's because she touched Aqua's Keyblade). Nonetheless, I think Ventus is more like Kairi than Sora, and Aqua is more like Sora than Kairi.