You are an angel that often stayed behind in Heaven, the youngest of angels. But you often hanged around the Garrison that Castiel commanded in hopes of gaining his attention. But nothing ever happened when you tried to earn his attention.

He went to Earth and rebelled, but you still adored and followed him. Helping and learning alongside humans to stand by his side. You managed to find Dean Winchester, the Righteous Man, when he was by himself and helped him. It was there that you learned how Castiel spoke about you, calling you a fledgling. Nothing else.

After helping you, you buried yourself in the apartment you acquired and stayed in bed, curled up and completely heartbroken. But soon, mating season for angels come, and you enter it for the first time. You stayed in bed, but when you hear the flutter of wings, you look up and find Castiel in your room. His massive, black wings flared in a mating presentation.

Castiel had always observed the little angel that constantly hovered and watched him in Heaven when he was a soldier. Your adorable small wings and how you often defended him in small ways against his superiors. Over time, you became his mate within his mind. But he couldn't claim you until you entered your first mating season, so you remained as his, his Fledgling. And when he sensed your grace reacting to the mating season, he didn't waste time and went to you.