by Noman Nasir
First let's talk about the differences between the angelic gears. Your party has two angelic gears in it. One is the true angel, Xenogears, and the other is the false man-made angel called Crescens. I like calling Xenogears a true angel because it got its power from the Wave Existence who I think is either a servant of God or is God. Crescens on the other hand, while having wings/feathered hands was an angel created by human hands (I remember in one of the side quests Emeralda remembers Kim referring to her as his and Elly's angel or something like that) and such is a false angel.
Throughout the game Fei's gear goes through some transformations. As Id-Weltall we see Fei in the form of a fallen angel or an angel of hell (hence the red color). Normally Weltall is not much different from most of the other gears. However, when Id becomes active we see it release its angelic wings. This was an attempt by the writers to show us that Id is the personality who has inherited the greatest portion of the Contact's power. Even though this was obvious, what I mean to say is that we learn that Id is the closest personality to having divine like powers in contrast to the regular Fei we play with.
Eventually we get to see Xenogears. In the beginning we see it as an all red gear since only Id has contacted the Wave Existence. Then when all three personalities make peace they come together to form the true Xenogears which had all of the Contact's and maybe the Wave Existence's power. Now if you think about the colors on this guy then you realize that it has Id's red color, Fei's blue color and (this is just speculation) the Coward's green color. It's important to note that red, blue and green are in the group of additive primary colors, which when put together can form white. White is the most common color seen on Xenogears. This symbolizes two things; the unity of Fei's personalities and the purification (baptism) of both pilot and gear. It also symbolizes a transformation of Id from a fallen angel to an angel of light.
Food for thought: Even though we only see two angelic wings coming out of Xenogears in the final FMV it important to notice that it has eight spikes on its back. Now why should it have these spikes on it at all? When Fei goes into infinity mode light in the form of wings comes out of these spikes. However, even though he has eight spikes only six wings appear. I've heard that in Christianity or Judaism or both the number of wings an angel has represents its rank. And the highest number is six for normal angels. Those with six wings are called the Seraphim. If this is true then that would mean that Xenogears is in the highest class of angels. This idea of it being in the highest class of anything could be a symbolism towards it being the most powerful gear ever.