CASTs in this game are referred to Androids. They are human friendly and are aids to humans. Also most CASTs were created by an owner to serve a family until it broke and often they were treated with the same respect as toys.
In Phantasy Star Universe (PSU), CASTs have an affinity for ranged weapons, such as guns, although they can play any role. CAST, along with Beasts and Newmans were created by Humans, and fought against each other for 500 years, until an alliance was created. CASTs control the planet Parum, and are known for treating Humans with contempt and an air of superiority.
Due to the high level of customization most CASTs no longer look like generic giant robots so some even appear to be cyborgs. Along with that fact some CAST players have even gone as far as to make there character look like characters from other games and shows such as Master Chief, William Dunbar, and Cyborg Ninja.
At level 20, CASTs gain the ability to use "SUV Weapons", which are massively-powerful weapons which may only be used once a gauge is filled up, either by taking or dealing damage.