Here's just an idea, based on an old story of mine, Sunset. It's obviously a bit more complex haha.

Willow found herself kidnapped when she was only a few months into her life. The young kitten was ripped away from her family and put in the custody of complete and utter strangers who believed she was ultra-powerful. They called themselves ShadowClan. She was not treated well. She was scratched and starved, her own mother didn't recognize her when they came to rescue her. Willow was brought back home, where they tried their best to heal her. They fatted her up. They easily healed her scratches, though they'd leave scars. But in no way could they clean the scars in her memory. Only one cat had been nice to her in ShadowClan. And she'd always be in his debt. But to everyone else in ShadowClan, she vowed revenge. Willow knows one thing that ShadowClan doesn't- she has no special powers whatsoever, only the will and courage to take revenge on those who did so many wrongings to her.