We don't need wings to fly ( an Ereri AU )

Titans roaming around the half destroyed city. These Titans weren't huge and don't eat people, but they certainly kill them by trapping them in crystals and crush the red and purple crystals into pieces along with the people inside. These Titans look almost like every other human being, only that they were half covered in their own crystals and have demonic red eyes that glowed in the dark.

Unlike the other world, humans didn't need gears to fly and attack these beasts. Each soldier who has the abilities or the brains to fight against the Titans were legally given wings as an extra pair of limbs. Depending on that particular soldier, the wings grow accordingly and would have different advantages and disadvantages.

You'd expect in this chaotic situation, everyone would get along, right? Wrong. Humanity was split into two, the other illegal group consist of those who were either strictly against the ways of the officials, or were ones whose wing experiments had went too badly for them to fight.

Both fought the same enemy and had the same goal, so why don't they get along?