In this case you are Dean but you can choose your name and gender ofc. After Castiel and a bunch of other angels pulled you from hell Castiel felt drawn to you in some way. So he ended up kinda being your guardian angel. Protecting you on hunts, watching over you without you even knowing, making sure your taking care of yourself.

Castiel sits on the edge of your bed in you and your brothers motel room. Watching over you as you sleep.