Rustwood

ThunderClan tom with some WindClan blood, but he prefers to forget about it and most of ThunderClan has as well. 

He killed Ubavu's mother in a border skirmish where nobody should have been killed. Rustwood had gotten caught up in the tension and started the fight, but after it, he felt overwhelming guilt for his actions. He often sat in his nest wondering if the ShadowClan cat he'd killed had once had a big family who now missed her, or cats who depended on her. 

This was proven true when, many moons later, Ubavu found Rustwood while on a patrol and identified him as the cat who had killed her mother. Blinded by rage, she left the rest of the patrol to unleash her fury on Rustwood, and she eventually killed him in the pouring rain, which washed away their scents after. 

After a quick trial, Rustwood was sent to StarClan- before the incident, he had lived a happy life, and the positive parts of that life outweighed the negatives- killing a ShadowClan warrior.